INTEGRAL \int_0^{\pi/2} x^2 \ln^2\left(\cos(2 kx)\right)\,dx=\frac{11 \pi^5}{1440}
Today we will evaluate the beautiful integral found in this post We have (see appendix bellow for the proof) Then Appendix Recall the generating function Lets now focus only in the integral of the R.H.S. We then conclude that (A.1) Recall (A.2) (A.3) (A.4) On the other hand (A.5) Therefore (A.6) Squaring both sides of (A.6) we obtain (A.7) Now, let in (A.1), we obtain (A.8) Plugging the R.H.S. of (A.7) in the R.H.S. of (A.8) we get (A.9) Equating Real and Imaginary parts in (A.9) we obtain (A.10) (A.11) (A.11) Recall that , then Lets integrate by part the remaining integral, considering that Integrating by parts Therefore (A.12)