a) $$(a-3)(b+4) = ab + 4a - 3b -12$$
б) $$(x-7)(x+3) = x^2 + 3x - 7x -21 = x^2 - 4x -21$$
в) $$(2y+1)(5y-6) = 10y^2 -12y + 5y -6 = 10y^2 -7y -6$$
г) $$(4m^2+6)(4m-6) = 16m^3 -24m^2 + 24m -36$$
д) $$(3a-b)(2a-7b) = 6a^2 -21ab -2ab + 7b^2 = 6a^2 -23ab + 7b^2$$
е) $$(2x^2-x)(8x^2-2x) = 16x^4 -4x^3 - 8x^3 + 2x^2 = 16x^4 - 12x^3 + 2x^2$$
ж) $$(-a-1)(a^3+5) = -a^4 - 5a - a^3 - 5 = -a^4 - a^3 - 5a - 5$$