Question

cosx+cos3x=cos2x решить уравнение

Answer 1

2cos2xcosx-cos2x=0
cos2x*(2cosx-1)=0
cos2x=0⇒2x=π/2+πn⇒x=π/4+πn/2,n∈z
cosx=1/2⇒x=+-π/3+2πk,k∈z