Sin4x=-cos2x
2sin2xcos2x+cos2x=0
cos2x(2sin2x+1)=0
cos2x=0⇒2x=π/2+πn,n∈z
-π/2≤π/2+πn≤0
-1≤1+2n≤0
-2≤2n≤-1
-1≤n≤-1/2
n=-1⇒x=π/2-π=-π/2
sin2x=-1/2
1)sin2x=7π/6+2πk,k∈z⇒x=7π/12+πk,k∈z
-π/2≤7π/12+πk≤0
-6≤7+12k≤0
-13≤12k≤-7
-13/12≤k≤-7/12
k=-1⇒x=7π/12-π=-5π/12
2)sin2x=11π/6+2πm,m∈z⇒x=11π/12+πm,m∈z
-π/2≤11π/12+πm≤0
-6≤11+12m≤0
-17≤12m≤-11
-17/12≤m≤-11/12
m=-1⇒x=11π/12-π=-π/12
x=-π/2-наименьший