2cos^22x + 4= 9cos2x

Question

2cos^22x + 4= 9cos2x

Answer 1

Заменим cos2x на t
2t²-9t+4=0
D=81-32=49
t1=(9-7)/4= 1/2
t2=(9+7)/4=4
cos2x=1/2
2x=2Пn+П/3
x1=Пn1+П/6 n1∈z
cos2x=4
x2=Пn2+1/2 arccos(4) n2∈z