Cos² x- cos x - 2 = 0

Question

Cos² x- cos x - 2 = 0

Answer 1

Cosx=a
a²-a-2=0
a1+a2=1 U a1*a2=-2
a1=-1⇒cosx=-1⇒x=π+2πn,n∈z
a2=2⇒cosx=2>1 нет решения