<span>2a(a-b)+4ab=2a(a+b)
Упрощаем левую часть
</span><span>2a(a-b)+4ab=2а²-2ab+4ab=2a²+2ab
</span><span>Упрощаем правую часть
</span><span>2a(a+b)=2а²+2ab
</span>
2a²+2ab=<span>2a²+2ab
Тождество доказано
</span>
Cos x/2 = -1/2
x/2 = ±π/3 + 2πn, n∈Z
x = <span>±2</span>π/3 + 4πn, n∈Z
..................... .....
X=0
y=4*0-10=-10
y=0
4x-10=0
4x=10
x=2,5
(0;-10);(2,5;0)