a) $$ (x + 6)(x + 5) = x^2 + 5x + 6x + 30 = x^2 + 11x + 30 $$
б) $$ (a - 4)(a + 1) = a^2 + a - 4a - 4 = a^2 - 3a - 4 $$
в) $$ (2 - y)(y - 8) = 2y - 16 - y^2 + 8y = -y^2 + 10y - 16 $$
г) $$ (a - 4)(2a + 1) = 2a^2 + a - 8a - 4 = 2a^2 - 7a - 4 $$
д) $$ (2y - 1)(3y + 2) = 6y^2 + 4y - 3y - 2 = 6y^2 + y - 2 $$
e) $$ (5x - 3)(4 - 3x) = 20x - 15x^2 - 12 + 9x = -15x^2 + 29x - 12 $$
Ответ: смотри решение