3tg(5pi/6 -2x)+√3=0
3tg(5pi/6 -2x)=-√3
tg(5pi/6 -2x)=-1/√3
5pi/6 -2x=arctg(-1/√3)+pi*n
5pi/6 -2x=5pi/6 +pi*n
-2x=pi*n
x=-pi*n/2
X^2-2x+x+2-x^2= -x+2
<span>7x^2-4x-24+-x^2= 6х^2-4х-24
</span>7x^2-6x-11+-x^2-2x+13= 6х^2-8х+2
2x^2-8x+13+(x-5)^2= 2x^2-8x+13+х^2-10х+25= 3х^2-18х+38
<span>(x+1)^2+(x-2)^2= х^2+2х+1+х^2-4х+4= 2х^2-2х+5
</span><span>(x-10)^2+(1-x)^2= х^2-20х+100+1-2х+х^2= 2х^2-22х+101
</span>Вот так вот
Sin²α+cos²α=1
sin²α=1-cos²α
sin²α=1-16/25
sin²α=9/25
/sinα/=3/5
α∈(π/2,π) : sinα=3/5
tgα=sinα/cosα, tgα=3/4
cos2α=cos²α-sin²α=16/25 - 9/25
cos2α=7/25