(a-5)(a+2) = a^2 + 2a - 5a - 10 = a^2 - 3a - 10
(2х+7у)(3х-у) = 2x3x + 2x(-y) + 7y3x + 7y(-y) = 6x^2 - 2xy + 21xy - 7y^2 = 6x^2 + 19xy - 7y^2
(a-5)(a+2) = a^2 + 2a - 5a - 10 = a^2 - 3a - 10
(2х+7у)(3х-у) = 2x3x + 2x(-y) + 7y3x + 7y(-y) = 6x^2 - 2xy + 21xy - 7y^2 = 6x^2 + 19xy - 7y^2