Y^-10y+25-y^+28y=-11
18y=-36
Y=-2
9x-4x-12=5x-12. левая часть равна правой. тождество доказано.
xy^2 - x - y^2 + 1 =
= x(y^2 - 1) - 1(y^2 - 1) =
= (x - 1)(y^2 - 1) =
= (x - 1)(y - 1)(y + 1)
5x^2 + 4x - 1 = 0
D = b^2 + 4ac = 16 + 20 = 36
x1 = ( - 4 + 6)/10 = 2/10 = 1/5 = 0,2
x2 = ( - 4 - 6)/10 = - 10/10 = - 1