Question

Cosx(-1-2cosx)=0 на промежутке [-3пи/2 ; 0]

Answer 1

COSX(-1)-2COS^2X=0

 

COSX-2COS^2X=0 

COSX-2(1+COS2x/2)=0

cosx-1+cos2x=0

cosx+cos2x=1

cosx+(cos^2x-sin^2x)=cos^2x+sin^2x

cosx+cos^2x-sin^2x-cos^2x+sin^2x=0

cosx=0