Answer:
[tex] \displaystyle \sin (x) - \frac{ { \sin}^{3} (x)}{3} + \rm C[/tex]
Step-by-step explanation:
we would like to integrate the following integration
[tex] \displaystyle \int \cos ^{3} (x) dx[/tex]
in order to do so rewrite
[tex] \displaystyle \int \cos ^{2} (x) \cos(x) dx[/tex]
we can also rewrite cos²(x) by using trigonometric indentity
[tex] \displaystyle \int( 1 - \sin ^{2} (x) )\cos(x) dx[/tex]
to apply u-substitution we'll choose
[tex] \rm \displaystyle u = \sin ^{} (x) \quad \text{and} \quad du = \cos(x) dx[/tex]
thus substitute:
[tex] \displaystyle \int( 1 - {u}^{2} )du[/tex]
apply substraction integration and:
[tex] \displaystyle \int 1du - \int {u}^{2} du[/tex]
use constant integration rule:
[tex] \displaystyle u - \int {u}^{2} du[/tex]
use exponent integration rule:
[tex] \displaystyle u - \frac{ {u}^{3} }{3} [/tex]
back-substitute:
[tex] \displaystyle \sin (x) - \frac{ { \sin}^{3} (x)}{3} [/tex]
finally we of course have to add constant of integration:
[tex] \displaystyle \sin (x) - \frac{ { \sin}^{3} (x)}{3} + \rm C[/tex]
