几道数学题求胜解,QAQ,
合并同类项:3(a-b)+4(a-b)-2(a-b)+6(a-b)=()
已知2x^2y与-1/3x^2my^3n是同类项,则4m^2-6mn+7的值等于()A9 B8 C7 D6
关于x,y的单项式3ax^3y^5与7bx^3y^5的和为0,则3a+7b=()