Упростите выражение:a)(3m-a)(a+3m)-(2a-m)(3a-m), б)(х-4y)(х+3y)+(х+3y)(3y+x)

a) (3m - a) * (a + 3m) - (2a - m) * (3a - m) = 3am + 9m^2 - a^2 - 3am - 6a^2 + 2am + 3am - m^2 = (3am - 3am + 2am + 3am) + (9m^2 - m^2) + (- a^2 - 6a^2) = 5am + 8m^2 - 7a^2 = 8m^2 + 5am - 7a^2.

Ответ: 8m^2 + 5am - 7a^2.

б) (x - 4y) * (x + 3y) + (x + 3y) * (3y + x) = x^2 + 3xy - 4xy -12y^2 + 3xy + x^2 + 9y^2 + 3xy = (x^2 + x^2) + (3xy - 4xy + 3xy + 3xy) + (-12y^2 + 9y^2) = 2x^2 + 5xy - 3y^2.

Ответ: 2x^2 + 5xy - 3y^2.