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