(1) Notice all even powers. Use power-to-frequency conversion:
Plug in:
Simplify:
(2) Reduce power again for
(This is derived from the power-to-frequency formula by changing ‘
(3) On the last term, swap even bunch:
Plug all in and obtain:
(4) Integrate the first three terms:
(5) Integrate the last term with
(6) Combine in final result:
Note: It is also possible to rewrite