Cos^2 x +13 cos x=14

Question

Cos^2 x +13 cos x=14

Answer 1

Cosx=a
a²+13a-14=0
a1+a2=-13 U a1*a2=-14
a1=-14⇒cosx=-14<-1 нет решения<br>a2=1⇒cosx=1⇒x=2πn,n∈z