Найдите ab, если a=c+3d,b=7c-4d

Question

Найдите ab, если a=c+3d,b=7c-4d

Answer 1

Ab=(c+3d)*(7c-4d)=7c^2-4dc+21dc-12d^2=7c^2+17dc-12d^2;ab=7c^2+17dc-12d^2