9y^2=6.25
y1= - 5/6
y2= 5/6
А7=а1+6d a11=a1+10d. тогда a11=a7+4d
-12=-6+4d -12+6=4d -6=4d d=-6/4=-1.5
a1= a7-6d=-6-6(-1.5)=-6+9=3
√(sin(π/3 - x/2)
sin(π/3 - x/2) ≥ 0
sin(x/2 - π/3) ≤ 0
- π - arcsin(0) + 2πk ≤ x/2 - π/3 ≤ arcsin(0) + 2πk, k∈Z
- π + 2πk ≤ x/2 ≤ 2πk, k∈Z
- π + π/3 + 2πk ≤ x/2 ≤ π/3 + 2πk, k∈Z
-2π/3 + 2πk ≤ x/2 ≤ π/3 + 2πk, k∈Z
-4π/3 +4πk ≤ x ≤ 2π/3 + 4πk, k∈Z