3a(a-b)+b(2a-b)=3a^2-3ab+2ab-b^2=3a^2-ab-b^2
3c(c-2)-(c-3)^2=3c^2-6c-(c^2-6c+9)=3c^2-6c-c^2+6c-9=2c^2-9
3a(a-b)+b(2a-b)=3a^2-3ab+2ab-b^2=3a^2-ab-b^2
3c(c-2)-(c-3)^2=3c^2-6c-(c^2-6c+9)=3c^2-6c-c^2+6c-9=2c^2-9