已知3x5+ay4和-5x3yb+1是同类项,求代数式3b4-6a3b-4b4+2ba3的值.
化简求值:-2a2b2+ab+5a2b2-ab-3a2b2,其中a=3,b=-4.
先化简,再求值:5x2-3y2-5x2+4y2+7xy,其中x=-1,y=1.
合并同类项:
(1)-a-a-a;
(2)3a2-5a2+9a2;
(3)2a2-3ab+4b2-5ab-6b2;
(4)xy-x2y2-xy-x2y2.
当k=____时,代数式x2 - 3kxy - 3y2+xy - 8中不含xy项.
单项式3abm与单项式nab2的和是9ab2,则m=______,n=______.