V=30-2t, v=6
6=30-2t
2t=30-6
2t=24
t=12с
√x³-4=11
x³-4≥0 U x³-4=121
x³≥4 U x³=125
x=5
5x+1≥0 U 1-x≥0
x≥-0,2 U x≤1
x∈[-0,2;1]
5x+1=1-2x+x²
x²-7x=0
x(x-7)=0
x=0 U x=7∉[-0,2;1]
Cos^2x-sin^2x=3+7cosx
cos^2x-1+cos^2x=3+7cosx
2cos^2x-7cosx-4=0
cosx=y,-1<=y<=1
2y^2-7y-4=0
D=49+32=81
y1=(7+9)/4=4
y2=(7-9)/4=-1/2
cosx=-1/2
x=+-2π/3+2πn