Помогите, пожалуйста))) 7sin^2 x+8cosx-8=0 [-пи/2;пи/2]

7(1-cos²x+8cosx-8=07cos²x-8cosx+1=0cosx=t7t²-8t+1=0a+b+c=0⇒t1=1 U t2=c/a7-8+1=0⇒t1=1 U t2=1/7cosx=1⇒x=2πn,n∈zn=-1⇒x=-2π∉[-π/2;π/2]n=0⇒x=0∈[-π/2;π/2]n=1⇒x=2π∉[-π/2;π/2]cosx=1/7⇒x=+-arccos1/7+2πn,n∈zпри n=0 x=-arccos1/7∈[-π/2;π/2] U x=arccos1/7∈[-π/2;π/2]