I know that this expression:
-(m-2 r+b^2 (-7 m+6 r)) ((-m+r)^2+b^4 (-2 m+3 r)^2+b^2 (-3 m^2+10 m r-6 r^2))+(1+b^2)^2 m^3 Cos[t]^2
Is equal to this one:
(1-3 b^2)^3 (-m+r)^2 (-m+2 r)+(1+b^2)^2 m^3 (b^2+Cos[t]^2)
I couldn't get Mathematica to reach this simpler later form. FullSimplify and other functions combinations like FullSimplify with PowerExpand didn't work. I even used VOISImplify, and no success. Any thoughts?