{"id":2972,"date":"2025-02-19T19:01:05","date_gmt":"2025-02-19T17:01:05","guid":{"rendered":"https:\/\/matematicastro.es\/?page_id=2972"},"modified":"2025-02-27T21:54:31","modified_gmt":"2025-02-27T20:54:31","slug":"ecuaciones-y-problemas-que-se-resuelven-planteando-ecuaciones-2","status":"publish","type":"page","link":"https:\/\/matematicastro.es\/?page_id=2972","title":{"rendered":"Ecuaciones y problemas que se resuelven planteando ecuaciones (2)"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><strong>Ejercicio 1.<\/strong> Resolver las siguientes ecuaciones<\/p>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-2914ce77703b5cf12fdc1861cc2d9fa8 wp-block-paragraph\"><strong>a)<\/strong> &nbsp;$\\displaystyle\\frac{\\displaystyle\\frac{1}{2}(x-4)}{6}-\\frac{2}{3}=1-\\frac{3(-2x+1)}{4}$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">$$\\frac{\\displaystyle\\frac{1}{2}(x-4)}{6}-\\frac{2}{3}=1-\\frac{3(-2x+1)}{4}\\Rightarrow \\frac{x-4}{12}-\\frac{2}{3}=1-\\frac{3(-2x+1)}{4}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Multiplicando por $12$ todos los t\u00e9rminos de la ecuaci\u00f3n:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x-4-8=12-9(-2x+1)\\Rightarrow x-12=12+18x-9\\Rightarrow -17x=15\\Rightarrow x=-\\frac{15}{17}$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-d66b934f8c708aa0018b1b4d88dc55bc wp-block-paragraph\"><strong>b) &nbsp;<\/strong>$\\displaystyle\\frac{\\displaystyle\\frac{2x}{3}+5}{5}=1-\\frac{\\displaystyle\\frac{1}{2}\\left(\\frac{3x}{4}-2\\right)}{3}$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">$$\\displaystyle\\frac{\\displaystyle\\frac{2x}{3}+5}{5}=1-\\frac{\\displaystyle\\frac{1}{2}\\left(\\frac{3x}{4}-2\\right)}{3}\\Rightarrow \\displaystyle\\frac{\\displaystyle\\frac{2x+15}{3}}{5}=1-\\frac{\\displaystyle\\frac{3x-8}{4}}{6}\\Rightarrow \\frac{2x+15}{15}=\\frac{3x-8}{24}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Multiplicando todos los t\u00e9rminos por $120$, que es el m\u00ednimo com\u00fan m\u00faltiplo de $24$ y $15$:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$8(2x+15)=120-5(3x-8)\\Rightarrow 16x+120=120-15x+40\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow 31x=40\\Rightarrow x=\\frac{40}{31}$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-c4ec45a04c0a50fd2b8dd0b92764655c wp-block-paragraph\"><strong>c) &nbsp;<\/strong>$\\displaystyle\\frac{1}{x^2-x}-\\frac{1}{x-1}=0$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">$$\\frac{1}{x^2-x}-\\frac{1}{x-1}=0\\Rightarrow \\frac{1}{x(x-1)}-\\frac{1}{x-1}=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Multiplicando todos los t\u00e9rminos por $x(x-1)$, tenemos:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\frac{x(x-1)}{x(x-1)}-\\frac{x(x-1)}{x-1}=0\\Rightarrow 1-x=0\\Rightarrow x=1$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pero para $x=1$ tendr\u00edamos la igualdad<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\frac{1}{0}-\\frac{1}{0}=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Igualdad que no tiene sentido. Por tanto la ecuaci\u00f3n&nbsp;$\\displaystyle\\frac{1}{x^2-x}-\\frac{1}{x-1}=0$ no tiene soluci\u00f3n.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-9e124a2a999199a40526630217b27e88 wp-block-paragraph\"><strong>d) &nbsp;<\/strong>$x^4-81x^2=0$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Para resolver esta ecuaci\u00f3n sacaremos factor com\u00fan $x^2$:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x^4-81x^2=0\\Rightarrow x^2(x^2-81)\\Rightarrow\\begin{cases}x^2=0\\Rightarrow x=0\\\\x^2-81=0\\Rightarrow x^2=81\\Rightarrow x=\\pm9\\end{cases}$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-d9fd0676ac14825012b85b14ea0ea92e wp-block-paragraph\"><strong>e) &nbsp;<\/strong>$\\displaystyle x^2+\\frac{4}{x^2}=5$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Multiplicando todos los t\u00e9rmios por $x^2$:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x^4+4=5x^2\\Rightarrow x^2-5x^2+4=0\\Rightarrow\\left(x^2\\right)^2-5x^2+4=0\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x^2=\\frac{5\\pm\\sqrt{(-5)^2-4\\cdot1\\cdot4}}{2\\cdot1}=\\frac{5\\pm\\sqrt{25-16}}{2}=\\frac{5\\pm\\sqrt{9}}{2}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{5\\pm3}{2}=\\begin{cases}\\frac{5+3}{2}=4\\Rightarrow x^2=4\\Rightarrow \\pm2\\\\ \\frac{5-3}{2}=1\\Rightarrow x^2=1\\Rightarrow x=\\pm1\\end{cases}$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-8a920a9b8e8b0c85c024c40617038b29 wp-block-paragraph\"><strong>f) &nbsp;<\/strong>$\\displaystyle \\frac{x^2(2x-5)}{x+1}=\\frac{9(1-x)}{2x+5}$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Obs\u00e9rvese que $1-x=-(x-1)$, con lo que la ecuaci\u00f3n la podemos escribir as\u00ed:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\frac{x^2(2x-5)}{x+1}=\\frac{-9(x-1)}{2x+5}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Multiplicando en cruz:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x^2(4x^2-25)=-9(x^2-1)\\Rightarrow 4x^4-25x^2=-9x^2+9\\Rightarrow 4x^4-16x^2-9=0\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow4\\left(x^2\\right)^2-16x-9=0\\Rightarrow x^2=\\frac{16\\pm\\sqrt{(-16)^2-4\\cdot4\\cdot(-9)}}{2\\cdot4}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{16\\pm\\sqrt{256+144}}{8}=\\frac{16\\pm\\sqrt{400}}{8}=\\frac{16\\pm20}{8}=\\begin{cases}\\frac{16+20}{8}=\\frac{36}{8}=\\frac{9}{2}\\\\ \\frac{16-20}{8}=-\\frac{4}{8}=-\\frac{1}{2}\\end{cases}\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow\\begin{cases}x^2=\\frac{9}{2}\\Rightarrow x=\\pm\\frac{3}{\\sqrt{2}}=\\pm\\frac{3\\sqrt{2}}{2}\\\\x^2=-\\frac{1}{2}\\Rightarrow \\nexists\\, x\\in\\mathbb{R}:x^2=-\\frac{1}{2}\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La ecuaci\u00f3n original tiene por tanto dos soluciones: $\\displaystyle\\frac{3\\sqrt{2}}{2}\\approx2,12$;&nbsp;$\\displaystyle-\\frac{3\\sqrt{2}}{2}\\approx-2,12$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-98cc654cbed7614cc4557cd1fc5c6684 wp-block-paragraph\"><strong>g) &nbsp;<\/strong>$\\displaystyle \\frac{1}{x^2}+\\frac{x^2}{3}=\\frac{28}{3x}$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Multiplicando todos los terminos por $3x^2$:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$3+x^4=28x\\Rightarrow x^4-28x+3=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La ecuaci\u00f3n anterior no es bicuadrada. Hemos de intentar pues buscar las ra\u00edces del polinomio $x^4-28x+3$ (que ser\u00e1n tambi\u00e9n las soluciones de la ecuaci\u00f3n anterior). Como se sabe, las ra\u00edces enteras han de ser divisores del t\u00e9rmino independiente, es decir, de $3$. Como $3^4-28\\cdot3+3=81-84+3=0$, por el teorema del resto, $x=3$ es una ra\u00edz de&nbsp;$x^4-28x+3$ (y por tanto tambi\u00e9n una soluci\u00f3n de la ecuaci\u00f3n). Aplicando la regla de Ruffini:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\begin{array}{c|rrrrr}<br>&amp; 1 &amp; 0 &amp; 0 &amp; -28 &amp; 3 \\\\ 3 &amp;  &amp; 3 &amp; 9 &amp; 27 &amp; -3 \\\\<br>\\hline<br>&amp; 1 &amp; 3 &amp; 9 &amp; -1 &amp; 0 \\\\ \\end{array}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Entonces&nbsp;$x^4-28x+3=(x-3)(x^3+3x^2+9x-1)$. El polinomio $x^3+3x^2+9x-1$ no tiene ra\u00edces enteras pues no lo son ni $1$, ni&nbsp;$-1$ (\u00a1compru\u00e9bese!). Como tampoco disponemos de ning\u00fan m\u00e9todo para resolver una ecuaci\u00f3n de tercer grado, concluimos que la soluci\u00f3n de la ecuaci\u00f3n es $x=3$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-8e4088fd735f0310ec1623203465e903 wp-block-paragraph\"><strong>h)&nbsp;<\/strong> $6+\\sqrt{2x+3}=x$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">$$6+\\sqrt{2x+3}=x\\Rightarrow\\sqrt{2x+3}=x-6\\Rightarrow(x-6)^2=\\sqrt{2x+3}^2\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow x^2-12x+36=2x+3\\Rightarrow x^2-14x+33=0\\Rightarrow$$ <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow x=\\frac{14\\pm\\sqrt{(-14)^2-4\\cdot1\\cdot33}}{2\\cdot1}=\\frac{14\\pm\\sqrt{196-132}}{2}=\\frac{14\\pm\\sqrt{64}}{2}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{14\\pm8}{2}=\\begin{cases}x_1=11\\\\x_2=3\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$x=11$ s\u00ed que es soluci\u00f3n pues satisface la ecuaci\u00f3n inicial:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$6+\\sqrt{2\\cdot11+3}=6+\\sqrt{22+3}=6+\\sqrt{25}=6+5=11$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$x=3$ no es soluci\u00f3n pues no satisface la ecuaci\u00f3n inicial:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$6+\\sqrt{2\\cdot3+3}=6+\\sqrt{6+3}=6+\\sqrt{9}=6+3=9$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-c2fc28c34976ea171d7dc62eeb960bcd wp-block-paragraph\"><strong>i) &nbsp;<\/strong>$\\sqrt{9-x}=\\sqrt{6-x}+\\sqrt{3}$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Elevando al cuadrado ambos miembros de la igualdad:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\left(\\sqrt{9-x}\\right)^2=\\left(\\sqrt{6-x}+\\sqrt{3}\\right)^2\\Rightarrow 9-x=6-x+2\\sqrt{3}\\sqrt{6-x}+3\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow 2\\sqrt{18-3x}=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Volviendo a elevar al cuadrado:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\left(2\\sqrt{18-3x}\\right)^2=0^2\\Rightarrow4(18-3x)=0\\Rightarrow72-12x=0\\Rightarrow-12x=-72\\Rightarrow x=6$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Efectivamente $x=6$ es soluci\u00f3n pues verifica la ecuaci\u00f3n inicial:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\sqrt{9-6}=\\sqrt{3}\\quad;\\quad\\sqrt{6-6}+\\sqrt{3}=0+\\sqrt{3}=\\sqrt{3}$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-7ae0258a0ddf6047e079f6a835347416 wp-block-paragraph\"><strong>j) &nbsp;<\/strong>$\\displaystyle\\sqrt{\\frac{x+1}{x-1}}=2$<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Esta es muy f\u00e1cil pues queda una ecuaci\u00f3n de primer grado elevando ambos miebros al cuadrado:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\left(\\sqrt{\\frac{x+1}{x-1}}\\right)^2=2^2\\Rightarrow\\frac{x+1}{x-1}=4\\Rightarrow x+1=4x-4\\Rightarrow-3x=-5\\Rightarrow x=\\frac{5}{3}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Efectivamente, $\\displaystyle x=\\frac{5}{3}$ es soluci\u00f3n pues<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\sqrt{\\frac{\\frac{5}{3}+1}{\\frac{5}{3}-1}}=\\sqrt{\\frac{\\frac{8}{3}}{\\frac{2}{3}}}=\\sqrt{\\frac{24}{6}}=\\sqrt{4}=2$$<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<hr class=\"wp-block-separator has-text-color has-vivid-red-color has-alpha-channel-opacity has-vivid-red-background-color has-background\"\/>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Ejercicio 2.<\/strong> Resuelve los siguientes problemas. Para ello plantea la ecuaci\u00f3n adecuada en cada uno de ellos.<\/p>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-36f448f1f462a173f5fb0b386600cffc wp-block-paragraph\"><strong>a) &nbsp;<\/strong>Determina dos n\u00fameros enteros consecutivos cuyo producto sea $380$.<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Dos n\u00fameros enteros consecutivos son, por ejemplo, $x$ y $x+1$. As\u00ed pues:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x(x+1)=380\\Rightarrow x^2+x=380\\Rightarrow x^2+x-380=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Resolviendo la ecuaci\u00f3n de segundo grado:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x=\\frac{-1\\pm\\sqrt{1^2-4\\cdot1\\cdot(-380)}}{2\\cdot1}=\\frac{-1\\pm\\sqrt{1+1520}}{2}=\\frac{-1\\pm\\sqrt{1521}}{2}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{-1\\pm39}{2}=\\begin{cases}x_1=\\frac{-1+39}{2}=\\frac{38}{2}=19\\\\x_2=\\frac{-1-39}{2}=\\frac{-40}{2}=-20\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Por tanto, hay dos posibles soluciones.&nbsp;Que los dos n\u00fameros sean $x=19$ y $x+1=20$.&nbsp;O bien que ambos n\u00fameros sean $x=-20$ y $x+1=-19$. Obs\u00e9rvese que en ambos casos el producto es $380$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-7202f394f3f4a5d918f1984cb479b02f wp-block-paragraph\"><strong>b) &nbsp;<\/strong>Encuentra las dimensiones de un rect\u00e1ngulo cuya \u00e1rea es $360\\,\\text{m}^2$ y cuyo per\u00edmetro mide $78\\ \\text{m}$.<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Supongamos que $a$ es la medida de un lado y que $b$ es la medida del otro.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Entonces el per\u00edmetro es $a+b+a+b=2a+2b$. Como \u00e9ste mide $78\\ \\text{m}$, entonces $2a+2b=78$, de donde, dividiendo todos los t\u00e9rminos entre $2$, $a+b=39$, es decir $b=39-a$.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Por otro lado, el \u00e1rea es&nbsp;$360\\,\\text{m}^2$ O sea:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$ab=360\\Rightarrow a(39-a)=360\\Rightarrow 39a-a^2=360\\Rightarrow a^2-39a+360=0$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Resolviendo esta ecuaci\u00f3n de segundo grado:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$a=\\frac{39\\pm\\sqrt{(-39)^2-4\\cdot1\\cdot360}}{2\\cdot1}=\\frac{39\\pm\\sqrt{1521-1440}}{2}=\\frac{39\\pm\\sqrt{81}}{2}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{39\\pm9}{2}=\\begin{cases}a_1=\\frac{39+9}{2}=\\frac{48}{2}=24\\\\a_2=\\frac{39-9}{2}=\\frac{30}{2}=15\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Si $a=24$, $b=39-a=39-24=15$. Si $a=15$, $b=39-a=39-15=24$. En cualquier caso el lado mayor del rect\u00e1ngulo mide&nbsp;$24\\ \\text{m}$ y el lado menor&nbsp;$15\\ \\text{m}$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-e3cd7997aea6c4636be37739b74db2af wp-block-paragraph\"><strong>c) &nbsp;<\/strong>Encuentra la longitud del lado de un cuadrado que tiene la misma \u00e1rea que un c\u00edrculo de un metro de radio. \u00bfQu\u00e9 tipo de n\u00famero es el resultado? Redondea el resultado a dos decimales.<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">El \u00e1rea $A$ del c\u00edrculo es $A=\\pi\\cdot r^2$, donde $r$ es el radio del mismo. Como nuestro c\u00edrculo tiene radio $1\\ \\text{m}$, entonces el \u00e1rea del c\u00edrculo es&nbsp;$A=\\pi\\cdot1^2=\\pi\\ \\text{m}^2$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Llamemos ahora $l$ al lado del cuadrado. Su \u00e1rea es $l^2$, que ha de ser igual al \u00e1rea del c\u00edrculo, con lo que:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$l^2=\\pi\\Rightarrow l=\\sqrt{\\pi}\\ \\text{m}^2$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Por supuesto el resultado es un n\u00famero irracional. Con la calculadora podemos redondear el resultado a dos decimales: $\\sqrt{\\pi}\\approx1,77\\ \\text{m}^2$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-a21840c60b91156f07c5d376b1ecec95 wp-block-paragraph\"><strong>d) &nbsp;<\/strong>Las medidas de los lados de un tri\u00e1ngulo rect\u00e1ngulo son tres n\u00fameros consecutivos. Encuentra el per\u00edmetro del tri\u00e1ngulo.<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Sean $x$,&nbsp;$x+1$,&nbsp;$x+2$ las medidas de los tres lados del tri\u00e1ngulo. El mayor de ellos,&nbsp;$x+2$, ha de ser la hipotenusa. Por el teorema de Pit\u00e1goras:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$(x+2)^2=x^2+(x+1)^2$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Desarrollando y resolviendo la ecuaci\u00f3n de segundo grado que resulta, tenemos:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$x^2+4x+4=x^2+x^2+2x+1\\Rightarrow x^2-2x-3=0\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow x=\\frac{2\\pm\\sqrt{(-2)^2-4\\cdot1\\cdot(-3)}}{2\\cdot1}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{2\\pm\\sqrt{4+12}}{2}=\\frac{2\\pm\\sqrt{16}}{2}=\\frac{2\\pm4}{2}=\\begin{cases}x_1=3\\\\x_2=-1\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La soluci\u00f3n $x=-1$ no es una soluci\u00f3n v\u00e1lida a nuestro problema pues un tri\u00e1ngulo no puede tener un lado de medida negativa.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De este modo las medidas de los lados del tri\u00e1ngulo rect\u00e1ngulo son $x=3$,&nbsp;$x+1=4$ y&nbsp;$x+2=5$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n\n\n\n<p class=\"has-black-color has-text-color has-link-color wp-elements-30c74b96c10af904c200dfd1133b10d8 wp-block-paragraph\"><strong>e) &nbsp;<\/strong>Un m\u00f3vil ha recorrido $120\\,\\text{km}$ Calcula su velocidad sabiendo que, si hubiera ido $10\\,\\text{km\/h}$ m\u00e1s r\u00e1pido, habr\u00eda tardado una hora menos.<\/p>\n\n\n\n<details class=\"wp-block-details has-background is-layout-flow wp-block-details-is-layout-flow\" style=\"background-color:#eafeec\"><summary>Soluci\u00f3n<\/summary>\n<p class=\"wp-block-paragraph\">Supondremos que se trata de un movimiento rectil\u00edneo y uniforme en el que $\\displaystyle v=\\frac{s}{t}$, donde $v$ es la velocidad en $\\text{km\/h}$, $s$ el espacio recorrido en $\\text{km}$ y $t$ el tiempo en horas empleado en recorrerlo.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Como el m\u00f3vil ha recorrido&nbsp;$120\\,\\text{km}$, entonces:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\displaystyle v=\\frac{120}{t}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Adem\u00e1s,&nbsp;si hubiera ido $10\\,\\text{km\/h}$ m\u00e1s r\u00e1pido, habr\u00eda tardado una hora menos, es decir:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$v+10=\\frac{120}{t-1}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Sustituyendo en esta \u00faltima expresi\u00f3n $v$ por su valor tenemos:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\frac{120}{t}+10=\\frac{120}{t-1}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Multiplicando todos los t\u00e9rminos por $t(t-1)$:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$120(t-1)+10t(t-1)=120t\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow 120t-120+10t^2-10t=120t\\Rightarrow10t^2-10t-120=0\\Rightarrow$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$\\Rightarrow t^2-t-12=0\\Rightarrow t=\\frac{1\\pm\\sqrt{(-1)^2-4\\cdot1\\cdot(-12)}}{2\\cdot1}=\\frac{1\\pm\\sqrt{1+48}}{2}=$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">$$=\\frac{1\\pm\\sqrt{49}}{2}=\\frac{1\\pm7}{2}=\\begin{cases}t_1=4\\\\t_2=-3\\end{cases}$$<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La soluci\u00f3n $t=-3$ no es v\u00e1lida para nuestro problema, pues el tiempo no puede tomar un valor negativo.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Por tanto tendremos que el tiempo empleado en recorrer los&nbsp;$120\\,\\text{km}$ ha sido de&nbsp;$t=4$ horas, a una velocidad de $\\displaystyle v=\\frac{120}{4}=30\\ \\text{km\/h}$.<\/p>\n\n\n\n<hr style=\"border: none; height: 1px; background-color: green;\">\n<\/details>\n","protected":false},"excerpt":{"rendered":"<p>Ejercicio 1. Resolver las siguientes ecuaciones a) &nbsp;$\\displaystyle\\frac{\\displaystyle\\frac{1}{2}(x-4)}{6}-\\frac{2}{3}=1-\\frac{3(-2x+1)}{4}$ b) &nbsp;$\\displaystyle\\frac{\\displaystyle\\frac{2x}{3}+5}{5}=1-\\frac{\\displaystyle\\frac{1}{2}\\left(\\frac{3x}{4}-2\\right)}{3}$ c) &nbsp;$\\displaystyle\\frac{1}{x^2-x}-\\frac{1}{x-1}=0$ d) &nbsp;$x^4-81x^2=0$ e) &nbsp;$\\displaystyle x^2+\\frac{4}{x^2}=5$ f) &nbsp;$\\displaystyle \\frac{x^2(2x-5)}{x+1}=\\frac{9(1-x)}{2x+5}$ g) &nbsp;$\\displaystyle \\frac{1}{x^2}+\\frac{x^2}{3}=\\frac{28}{3x}$ h)&nbsp; $6+\\sqrt{2x+3}=x$ i) &nbsp;$\\sqrt{9-x}=\\sqrt{6-x}+\\sqrt{3}$ j) &nbsp;$\\displaystyle\\sqrt{\\frac{x+1}{x-1}}=2$ Ejercicio 2. Resuelve los siguientes problemas. Para ello plantea la ecuaci\u00f3n adecuada en cada uno de ellos. a) &nbsp;Determina dos n\u00fameros enteros consecutivos cuyo producto sea [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2972","page","type-page","status-publish","hentry","post"],"_links":{"self":[{"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/pages\/2972","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/matematicastro.es\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2972"}],"version-history":[{"count":36,"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/pages\/2972\/revisions"}],"predecessor-version":[{"id":3446,"href":"https:\/\/matematicastro.es\/index.php?rest_route=\/wp\/v2\/pages\/2972\/revisions\/3446"}],"wp:attachment":[{"href":"https:\/\/matematicastro.es\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2972"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}