cos²x+2sinx+2=0
1-sin²x+2sinx+2=0
sinx=a
a²-2a-3=0
a1+a2=2 U a1*a2=-3
a1=-1⇒sinx=-1⇒x=-π/2+2πn
-4π≤-π/2+2πn≤2π
-8≤-1+4n≤4
-7≤4n≤5
-7/4≤n≤5/4
n=-1⇒x=-π/2-2π=-5π/2
n=0πx=-π/2
n=1πx=-π/2+2π=3π/2
a2=3⇒sinx=3>1
