2*16^cosx -9*4^cosx +4=0

Question

2*16^cosx -9*4^cosx +4=0

Answer 1

4^cosx=t. 2t^2-9t+4=0. d=81-4*2*4=49. t1=9-7/2*4=1/4. t2=9+7/2*4=2. cosx=1/2=+-p/3+2pk