1.выполните действия: 1)(х+у)(х-13) 2)(m+18)*(y+3) 3)(m+12)*(y-3) 2.найдите сумму многочленов: (3m^2+5mn++-3m^2)

№1
1) (х+у)(х-13) = х*х-х*13+ух*13 = х²-13х+ху-13у
2) (m+18)*(y+3) = my+3m+18y+18*3 = my+3m+18y+54
2) (m+12)*(y-3) = my-m*3-12y-12*3 = my-3m+12y-36

№2
(3m²+5mn+7m²y)-(5mn+3m²)-(7m³y-3m²) = 3m²+5mn+7m²y-5mn-3m²-7m³y+3m² = 7m²y-7m³y+3m²