Sin120°+cos150°-ctg30°=
sin(180°-60°)+cos(180°-30°)-ctg30°=
sin60°-cos30°-ctg30°=
√3/2-√3/2-√3=-√3
X+y=12 x=12-y
xy = 96 12y-y^2=96
-y^2+12y-96=0
y^2-12y+96=0
D= 12^2-4*1*96=144-384 d<0
решений нет
Cos x/2 = -1/2
x/2 = ±π/3 + 2πn, n∈Z
x = <span>±2</span>π/3 + 4πn, n∈Z
Корень из 169 будет 13
13*13=169