# Math Help - trig

1. ## trig

verify the identity: cos5t-cos3t= -8sin(squared)t[(2cos(cubed)t-cost)]

2. Hello,

cos(5t)=cos(4t+t)=cos(4t)cos(t)-sin(4t)sin(t)

cos(4t)=cos(2*2t)=2cos²(2t)-1
sin(4t)=sin(2*2t)=2cos(2t)sin(2t)

Continue and finish it...

There had to be a relation that can simplify, but i can't get on it anymore...