(7-y)^2-y^2=63
x=7-y
49-14y+y2-y2=63
x=7-y
y=-1
x=8
1-ctg2a*tga/tgactga=1-ctg2a*tga=1-1/tg2a*tga=1-(1-tg²a)/2tga*tga=1-(1-tg²a)/2=
=1-1/2+1/2*tg²a=1/2+1/2*tg²a=1/2(1+tg²a)=1/2*1/cos²a=1/2cos²a
-8x^2+14x-8=0
8x^2-14+8=0
4x^2-7x+4=0
D=49-256
D<0
Корней нет
Вот............................................
Решение
<span>Решите квадратное уравнение:
5х - 2 / 7х^2 = 0, x </span>≠ 0<span>
35x</span>³ - 2 = 0
35x³ = 2
x₁ = - ∛(2/35)
x₂ = ∛(2/35)
<span>
</span>