Para hallar los extremos hay que resolver la ecuación
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(la derivada es igual a cero),
y las raíces de esta ecuación serán los extremos de esta función:
$$\frac{d}{d x} f{\left(x \right)} = $$
primera derivada$$- \frac{3 x^{2} \left(\left(x^{2} + 4 x\right) + 8\right)}{\left(x^{3} + 27\right)^{2}} + \frac{2 x + 4}{x^{3} + 27} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -2 - \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}$$
$$x_{2} = -2 + \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}$$
Signos de extremos en los puntos:
2
/ _____________________________________________________________________________________________________________________________________\
| / _____________________ |
| / / ________ |
| / 32 / 1849 3*\/ 372585 172 |
| / - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |
| ___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ |
| / _____________________ / / ________ / _____________________ |
| / / ________ / / 1849 3*\/ 372585 / / ________ |
| / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 |
| / 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- |
| / \/ 4 4 _____________________ / / \/ 4 4 _____________________ |
_____________________________________________________________________________________________________________________________________ | / / ________ / / / ________ | _____________________________________________________________________________________________________________________________________ ___________________________________________________________
/ _____________________ | / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 | / _____________________ / _____________________
/ / ________ | / 3 / ---- + ------------ / / 3 / ---- + ------------ | / / ________ / / ________
/ 32 / 1849 3*\/ 372585 172 | \/ \/ 4 4 \/ \/ \/ 4 4 | / 32 / 1849 3*\/ 372585 172 / / 1849 3*\/ 372585 32
/ - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |-2 + --------------------------------------------------------------------- - ----------------------------------------------------------------------------------------------------------------------------------------------------| - 2* / - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- + 2* / 2*3 / ---- + ------------ + --------------------------
___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ \ 2 2 / / _____________________ \/ 4 4 ___________________________________________________________ / \/ 4 4 _____________________
/ _____________________ / / ________ / _____________________ / / ________ / _____________________ / / ________
/ / ________ / / 1849 3*\/ 372585 / / ________ / / 1849 3*\/ 372585 / / ________ / / 1849 3*\/ 372585
/ / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 / 3 / ---- + ------------
/ 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- \/ \/ 4 4
/ \/ 4 4 _____________________ / / \/ 4 4 _____________________ / / \/ 4 4 _____________________
/ / ________ / / / ________ / / / ________
/ / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585
/ 3 / ---- + ------------ / / 3 / ---- + ------------ / / 3 / ---- + ------------
\/ \/ 4 4 \/ \/ \/ 4 4 \/ \/ \/ 4 4
(-2 + --------------------------------------------------------------------- - ----------------------------------------------------------------------------------------------------------------------------------------------------, -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------)
2 2 3
/ _____________________________________________________________________________________________________________________________________\
| / _____________________ |
| / / ________ |
| / 32 / 1849 3*\/ 372585 172 |
| / - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |
| ___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ |
| / _____________________ / / ________ / _____________________ |
| / / ________ / / 1849 3*\/ 372585 / / ________ |
| / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 |
| / 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- |
| / \/ 4 4 _____________________ / / \/ 4 4 _____________________ |
| / / ________ / / / ________ |
| / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 |
| / 3 / ---- + ------------ / / 3 / ---- + ------------ |
| \/ \/ 4 4 \/ \/ \/ 4 4 |
27 + |-2 + --------------------------------------------------------------------- - ----------------------------------------------------------------------------------------------------------------------------------------------------|
\ 2 2 /
2
/ _____________________________________________________________________________________________________________________________________\
| / _____________________ |
| / / ________ |
| / 32 / 1849 3*\/ 372585 172 |
| / - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |
| ___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ |
| / _____________________ / / ________ / _____________________ |
| / / ________ / / 1849 3*\/ 372585 / / ________ |
| / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 |
| / 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- |
| / \/ 4 4 _____________________ / / \/ 4 4 _____________________ |
_____________________________________________________________________________________________________________________________________ | / / ________ / / / ________ | ___________________________________________________________ _____________________________________________________________________________________________________________________________________
/ _____________________ | / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 | / _____________________ / _____________________
/ / ________ | / 3 / ---- + ------------ / / 3 / ---- + ------------ | / / ________ / / ________
/ 32 / 1849 3*\/ 372585 172 | \/ \/ 4 4 \/ \/ \/ 4 4 | / / 1849 3*\/ 372585 32 / 32 / 1849 3*\/ 372585 172
/ - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |-2 + --------------------------------------------------------------------- + ----------------------------------------------------------------------------------------------------------------------------------------------------| + 2* / 2*3 / ---- + ------------ + -------------------------- + 2* / - -------------------------- - 2*3 / ---- + ------------ + ---------------------------------------------------------------------
___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ \ 2 2 / / \/ 4 4 _____________________ / _____________________ \/ 4 4 ___________________________________________________________
/ _____________________ / / ________ / _____________________ / / ________ / / ________ / _____________________
/ / ________ / / 1849 3*\/ 372585 / / ________ / / 1849 3*\/ 372585 / / 1849 3*\/ 372585 / / ________
/ / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / 3 / ---- + ------------ / / 1849 3*\/ 372585 32
/ 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- \/ \/ 4 4 / \/ 4 4 / 2*3 / ---- + ------------ + --------------------------
/ \/ 4 4 _____________________ / / \/ 4 4 _____________________ / / \/ 4 4 _____________________
/ / ________ / / / ________ / / / ________
/ / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585
/ 3 / ---- + ------------ / / 3 / ---- + ------------ / / 3 / ---- + ------------
\/ \/ 4 4 \/ \/ \/ 4 4 \/ \/ \/ 4 4
(-2 + --------------------------------------------------------------------- + ----------------------------------------------------------------------------------------------------------------------------------------------------, -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------)
2 2 3
/ _____________________________________________________________________________________________________________________________________\
| / _____________________ |
| / / ________ |
| / 32 / 1849 3*\/ 372585 172 |
| / - -------------------------- - 2*3 / ---- + ------------ + --------------------------------------------------------------------- |
| ___________________________________________________________ / _____________________ \/ 4 4 ___________________________________________________________ |
| / _____________________ / / ________ / _____________________ |
| / / ________ / / 1849 3*\/ 372585 / / ________ |
| / / 1849 3*\/ 372585 32 / 3 / ---- + ------------ / / 1849 3*\/ 372585 32 |
| / 2*3 / ---- + ------------ + -------------------------- / \/ 4 4 / 2*3 / ---- + ------------ + -------------------------- |
| / \/ 4 4 _____________________ / / \/ 4 4 _____________________ |
| / / ________ / / / ________ |
| / / 1849 3*\/ 372585 / / / 1849 3*\/ 372585 |
| / 3 / ---- + ------------ / / 3 / ---- + ------------ |
| \/ \/ 4 4 \/ \/ \/ 4 4 |
27 + |-2 + --------------------------------------------------------------------- + ----------------------------------------------------------------------------------------------------------------------------------------------------|
\ 2 2 /
Intervalos de crecimiento y decrecimiento de la función:Hallemos los intervalos donde la función crece y decrece y también los puntos mínimos y máximos de la función, para lo cual miramos cómo se comporta la función en los extremos con desviación mínima del extremo:
Puntos mínimos de la función:
$$x_{1} = -2 - \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}$$
Puntos máximos de la función:
$$x_{1} = -2 + \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}$$
Decrece en los intervalos
$$\left[-2 - \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}, -2 + \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}\right]$$
Crece en los intervalos
$$\left(-\infty, -2 - \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}\right] \cup \left[-2 + \frac{\sqrt{- 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}} - \frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + \frac{172}{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}}}{2} + \frac{\sqrt{\frac{32}{\sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}} + 2 \sqrt[3]{\frac{3 \sqrt{372585}}{4} + \frac{1849}{4}}}}{2}, \infty\right)$$