Подстановка условия
[src](x - y)^2 - (x - y)*(x - y) при y = -1
(x - y)^2 - (x - y)*(x - y)
$$\left(x - y\right)^{2} - \left(x - y\right)^{2}$$
(x - (-1))^2 - (x - (-1))*(x - (-1))
$$\left(- (-1) + x\right)^{2} - \left(- (-1) + x\right)^{2}$$
(x - (-1))^2 - (x - (-1))*(x - (-1))
$$\left(x - -1\right)^{2} - \left(x - -1\right)^{2}$$