Question

cos4x = 6cos^2x - 5 ;

cos2x = 3 + 7cosx

Answer 1

cos2X = 3 + 7cosX

2cos"2(X) -1 = 3 + 7cosX

2cos"2(X) - 7 cosX - 4 = 0

(cosX - 4)(2cosX +1) = 0

cosX=4 , cosX = -1/2

X=nevozmojno naiti (tak kak bolwe 1)  X = 120