Question

помогите 2cos2x + 4sin(3π/2 +x)-1=0

Answer 1

2cos2x-4cosx-1=0

4cos^2x-2-4cosx-1=0

cosx=t

4t^2-4t-3=0

t=(2+-4)/4

-1<=t<=1

t=-1/2

x=+-2П/3+2пk