Se da la desigualdad:
$$\left(2 x + \frac{\left(x + 5\right) \left(x + 7\right)^{2}}{x^{2}}\right) + 1 \leq 0$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\left(2 x + \frac{\left(x + 5\right) \left(x + 7\right)^{2}}{x^{2}}\right) + 1 = 0$$
Resolvemos:
$$x_{1} = - \frac{20}{9} + \frac{671}{27 \left(- \frac{1}{2} - \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}} - \frac{\left(- \frac{1}{2} - \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3}$$
$$x_{2} = - \frac{20}{9} - \frac{\left(- \frac{1}{2} + \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} + \frac{671}{27 \left(- \frac{1}{2} + \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
$$x_{3} = - \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{20}{9} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
Descartamos las soluciones complejas:
$$x_{1} = - \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{20}{9} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
Las raíces dadas
$$x_{1} = - \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{20}{9} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} \leq x_{1}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$\left(- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{20}{9} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}\right) + - \frac{1}{10}$$
=
$$- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{209}{90} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
lo sustituimos en la expresión
$$\left(2 x + \frac{\left(x + 5\right) \left(x + 7\right)^{2}}{x^{2}}\right) + 1 \leq 0$$
$$\left(2 \left(- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{209}{90} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}\right) + \frac{\left(\left(- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{209}{90} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}\right) + 5\right) \left(\left(- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{209}{90} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}\right) + 7\right)^{2}}{\left(- \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{209}{90} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}\right)^{2}}\right) + 1 \leq 0$$
2
/ ____________________ \ / ____________________ \
| / _____ | | / _____ |
| / 11275 77*\/ 309 | | / 11275 77*\/ 309 |
| 3 / ----- + ---------- | | 3 / ----- + ---------- |
|421 \/ 54 2 671 | |241 \/ 54 2 671 |
|--- - ------------------------- + ----------------------------| *|--- - ------------------------- + ----------------------------|
____________________ | 90 3 ____________________| | 90 3 ____________________|
/ _____ | / _____ | | / _____ |
/ 11275 77*\/ 309 | / 11275 77*\/ 309 | | / 11275 77*\/ 309 |
2*3 / ----- + ---------- | 27*3 / ----- + ---------- | | 27*3 / ----- + ---------- |
164 \/ 54 2 1342 \ \/ 54 2 / \ \/ 54 2 /
- --- - --------------------------- + ---------------------------- + ---------------------------------------------------------------------------------------------------------------------------------- <= 0
45 3 ____________________ 2
/ _____ / ____________________ \
/ 11275 77*\/ 309 | / _____ |
27*3 / ----- + ---------- | / 11275 77*\/ 309 |
\/ 54 2 | 3 / ----- + ---------- |
| 209 \/ 54 2 671 |
|- --- - ------------------------- + ----------------------------|
| 90 3 ____________________|
| / _____ |
| / 11275 77*\/ 309 |
| 27*3 / ----- + ---------- |
\ \/ 54 2 /
significa que la solución de la desigualdad será con:
$$x \leq - \frac{\sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}{3} - \frac{20}{9} + \frac{671}{27 \sqrt[3]{\frac{11275}{54} + \frac{77 \sqrt{309}}{2}}}$$
_____
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