5 sin^2x + 4sin (П/2 + х) = 4

5sin²x+4sin (π/2+x) = 4

5sin²x+4cosx=4

5 (1-cos²x) + 4cosx=4

5-5cos²x+4cosx-4=0

1-5cos²x+4cosx=0

5cos²x-4cosx-1=0

D=4²+1·5·4=16+20=36

cosx = (4 ± √36) / 10

cosx=1 или cosx=-1/5

x1=2πn, n∈Z

x2=π-arccos0,2+2πn

x3=arccos0,2-π+2πn