а) (5m+7n) (2n+4m) = 10mn + 14n^2 + 20m^2 + 28mn = 14n^2 + 20m^2 + 38mn
б) (2x-3y) (2x+3y) = 4x^2 - 6xy + 6xy - 9y^2 = 4x^2 - 9y^2
в) (-a-b) (2a-3b)= -2a^2 - 2ab + 3ab + 3b^2 = 3b^2 + ab - 2a^2
г) (a^2 + b^2)(a^2 + b^2)=a^4 + a^2b^2 + a^2b^2 + b^4 = a^4 + 2a^2b^2 + b^4
д) (2x^2 - y^2)(y^2 + 2x^2) =2x^2y^2 - y^4 + 4x^4 - 2x^2y^2 = 4x^4 - y^4