Se da la desigualdad:
$$-2 + \frac{\left(x - 2\right) \left(x + 5\right)^{2}}{\left(-1\right) x} > 0$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$-2 + \frac{\left(x - 2\right) \left(x + 5\right)^{2}}{\left(-1\right) x} = 0$$
Resolvemos:
$$x_{1} = - \frac{8}{3} + \left(- \frac{1}{2} - \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}} + \frac{43}{9 \left(- \frac{1}{2} - \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}}$$
$$x_{2} = - \frac{8}{3} + \frac{43}{9 \left(- \frac{1}{2} + \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \left(- \frac{1}{2} + \frac{\sqrt{3} i}{2}\right) \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
$$x_{3} = - \frac{8}{3} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
Descartamos las soluciones complejas:
$$x_{1} = - \frac{8}{3} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
Las raíces dadas
$$x_{1} = - \frac{8}{3} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{1}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + \left(- \frac{8}{3} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}\right)$$
=
$$- \frac{83}{30} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
lo sustituimos en la expresión
$$-2 + \frac{\left(x - 2\right) \left(x + 5\right)^{2}}{\left(-1\right) x} > 0$$
$$-2 + \frac{\left(-2 + \left(- \frac{83}{30} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}\right)\right) \left(\left(- \frac{83}{30} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}\right) + 5\right)^{2}}{\left(-1\right) \left(- \frac{83}{30} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}\right)} > 0$$
2
/ _________________ \ / _________________ \
| / _______ | | / _______ |
|67 / 415 \/ 10302 43 | | 143 / 415 \/ 10302 43 |
|-- + 3 / --- + --------- + ------------------------| *|- --- + 3 / --- + --------- + ------------------------|
|30 \/ 27 9 _________________| | 30 \/ 27 9 _________________|
| / _______ | | / _______ |
| / 415 \/ 10302 | | / 415 \/ 10302 |
| 9*3 / --- + --------- | | 9*3 / --- + --------- |
\ \/ 27 9 / \ \/ 27 9 /
-2 + --------------------------------------------------------------------------------------------------------------------- > 0
_________________
/ _______
83 / 415 \/ 10302 43
-- - 3 / --- + --------- - ------------------------
30 \/ 27 9 _________________
/ _______
/ 415 \/ 10302
9*3 / --- + ---------
\/ 27 9
significa que la solución de la desigualdad será con:
$$x < - \frac{8}{3} + \frac{43}{9 \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}} + \sqrt[3]{\frac{\sqrt{10302}}{9} + \frac{415}{27}}$$
_____
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