Выполнить умножение (a-3)(a+5) (4x-y)(5y+3x) (x-3)(x^2-2x+7) !

(a - 3)(a + 5) = a^2 + 5a - 3a - 15 = a^2 + 2a - 15 

(4x - y)(5y + 3x) = 20xy + 12x^2 - 5y^2 - 3xy = 12x^2 - 5y^2 + 17xy

(x - 3)(x^2 - 2x + 7) = x^2(x - 3) - 2x(x  - 3) + 7(x - 3) = 
= x^3 - 3x^2 - 2x^2 + 6x + 7x - 21 = 
= x^3 - 5x^2 +13 x - 21