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$$- \frac{12 x^{3} \left(3 x + \left(x^{4} + 1\right)\right)}{\left(3 x^{4} + 5\right)^{2}} + \frac{4 x^{3} + 3}{3 x^{4} + 5} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}}{2}$$
$$x_{2} = - \frac{\sqrt{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}}{2} + \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27}$$
Signos de extremos en los puntos:
4
/ _______________________________________________________________________________________________________________________________________________________________\ _______________________________________________________________________________________________________________________________________________________________
| / ______________________ | / ______________________
_______________________________________________________________________________________________________________________________________________________________ | / / _______ | / / _______
/ ______________________ | / 32 / 20 5*\/ 10951 10 128 | / 32 / 20 5*\/ 10951 10 128
/ / _______ | / --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- | 3* / --- - 2*3 / - ---- + ----------- + ------------------------------ + --------------------------------------------------------------------------------------
/ 32 / 20 5*\/ 10951 10 128 | ______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ | ______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________
/ --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- | / ______________________ / / _______ / ______________________ | / ______________________ / / _______ / ______________________
______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ | / / _______ / / 20 5*\/ 10951 / / _______ | / / _______ / / 20 5*\/ 10951 / / _______
/ ______________________ / / _______ / ______________________ | / 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 | / 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10
/ / _______ / / 20 5*\/ 10951 / / _______ | / --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ | 3* / --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------
/ 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 | / 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ | / 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________
/ --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ | / / _______ / / / _______ | / / _______ / / / _______
/ 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ | / / 20 5*\/ 10951 / / / 20 5*\/ 10951 | / / 20 5*\/ 10951 / / / 20 5*\/ 10951
/ / _______ / / / _______ | / 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- | / 27*3 / - ---- + ----------- / / 27*3 / - ---- + -----------
/ / 20 5*\/ 10951 / / / 20 5*\/ 10951 11 |2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 | \/ \/ 6561 6561 \/ \/ \/ 6561 6561
/ 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- -- + |-- + -------------------------------------------------------------------------------- + ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| + ---------------------------------------------------------------------------------- + --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 9 \27 2 2 / 2 2
(-- + -------------------------------------------------------------------------------- + ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------)
27 2 2 4
/ _______________________________________________________________________________________________________________________________________________________________\
| / ______________________ |
| / / _______ |
| / 32 / 20 5*\/ 10951 10 128 |
| / --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- |
| ______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ |
| / ______________________ / / _______ / ______________________ |
| / / _______ / / 20 5*\/ 10951 / / _______ |
| / 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 |
| / --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ |
| / 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ |
| / / _______ / / / _______ |
| / / 20 5*\/ 10951 / / / 20 5*\/ 10951 |
| / 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- |
|2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 |
5 + 3*|-- + -------------------------------------------------------------------------------- + ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
\27 2 2 /
4
/ _______________________________________________________________________________________________________________________________________________________________\ _______________________________________________________________________________________________________________________________________________________________
| / ______________________ | / ______________________
_______________________________________________________________________________________________________________________________________________________________ | / / _______ | / / _______
/ ______________________ | / 32 / 20 5*\/ 10951 10 128 | / 32 / 20 5*\/ 10951 10 128
/ / _______ | / --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- | 3* / --- - 2*3 / - ---- + ----------- + ------------------------------ + --------------------------------------------------------------------------------------
/ 32 / 20 5*\/ 10951 10 128 | ______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ | / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ ______________________________________________________________________
/ --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- | / ______________________ / / _______ / ______________________ | / / _______ / ______________________ / ______________________
______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ | / / _______ / / 20 5*\/ 10951 / / _______ | / / 20 5*\/ 10951 / / _______ / / _______
/ ______________________ / / _______ / ______________________ | / 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 | / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 / 16 / 20 5*\/ 10951 10
/ / _______ / / 20 5*\/ 10951 / / _______ | / --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ | / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ 3* / --- + 2*3 / - ---- + ----------- - ------------------------------
/ 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 | / 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ | / / 729 \/ 6561 6561 ______________________ / 729 \/ 6561 6561 ______________________
/ --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ | / / _______ / / / _______ | / / / _______ / / _______
/ 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ | / / 20 5*\/ 10951 / / / 20 5*\/ 10951 | / / / 20 5*\/ 10951 / / 20 5*\/ 10951
/ / _______ / / / _______ | / 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- | / / 27*3 / - ---- + ----------- / 27*3 / - ---- + -----------
/ / 20 5*\/ 10951 / / / 20 5*\/ 10951 11 |2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 | \/ \/ \/ 6561 6561 \/ \/ 6561 6561
/ 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- -- + |-- + -------------------------------------------------------------------------------- - ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| - -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- + ----------------------------------------------------------------------------------
2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 9 \27 2 2 / 2 2
(-- + -------------------------------------------------------------------------------- - ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------)
27 2 2 4
/ _______________________________________________________________________________________________________________________________________________________________\
| / ______________________ |
| / / _______ |
| / 32 / 20 5*\/ 10951 10 128 |
| / --- - 2*3 / - ---- + ----------- + ------------------------------ + -------------------------------------------------------------------------------------- |
| ______________________________________________________________________ / 729 \/ 6561 6561 ______________________ ______________________________________________________________________ |
| / ______________________ / / _______ / ______________________ |
| / / _______ / / 20 5*\/ 10951 / / _______ |
| / 16 / 20 5*\/ 10951 10 / 27*3 / - ---- + ----------- / 16 / 20 5*\/ 10951 10 |
| / --- + 2*3 / - ---- + ----------- - ------------------------------ / \/ 6561 6561 19683* / --- + 2*3 / - ---- + ----------- - ------------------------------ |
| / 729 \/ 6561 6561 ______________________ / / 729 \/ 6561 6561 ______________________ |
| / / _______ / / / _______ |
| / / 20 5*\/ 10951 / / / 20 5*\/ 10951 |
| / 27*3 / - ---- + ----------- / / 27*3 / - ---- + ----------- |
|2 \/ \/ 6561 6561 \/ \/ \/ 6561 6561 |
5 + 3*|-- + -------------------------------------------------------------------------------- - ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
\27 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:
$$x_{1} = - \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2} + \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27}$$
Puntos máximos de la función:
$$x_{1} = \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27} + \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2}$$
Decrece en los intervalos
$$\left[- \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2} + \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27}, \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27} + \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2}\right]$$
Crece en los intervalos
$$\left(-\infty, - \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2} + \frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27}\right] \cup \left[\frac{\sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}{2} + \frac{2}{27} + \frac{\sqrt{\left|{- 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}} + \frac{32}{729} + \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{128}{19683 \sqrt{- \frac{10}{27 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}} + \frac{16}{729} + 2 \sqrt[3]{- \frac{20}{6561} + \frac{5 \sqrt{10951}}{6561}}}}}\right|}}{2}, \infty\right)$$