(-5x - y)^2 - 10x(-7x + y) =
(-5x - y)(-5x - y) - 10x(-7x + y) (25x^2 + 10xy + y^2) - (-70x^2 + 10xy) 25x^2 + 10xy + y^2 + 70x^2 - 10xy 95x^2 + y^2
(-5x - y)^2 - 10x(-7x + y) =
(-5x - y)(-5x - y) - 10x(-7x + y)
(25x^2 + 10xy + y^2) - (-70x^2 + 10xy)
25x^2 + 10xy + y^2 + 70x^2 - 10xy
95x^2 + y^2