1)3a-2a+4-3a^2+a.=-3a^2+2a
2)xy+2xy-3x^2-3xv+x^2.=-2x^2
3)5a^2b-3ab-4ab^2+7ab-2ab^2.=5a^2b+4ab-6ab^2
4)4-2xy+7xy-15+xy=-11+6xy详细呀直接合并就可以了。这些不需要步骤了。老师要看步骤滴)3a-2a+4-3a^2+a.=-3a^2+（3-2+1）a=-3a^2+2a
2)xy+2xy-3x^2-3xv+x^2. =（-3+1）x^2+(1+2-3)xy)=-2x^2
3)5a^2b-3ab-4ab^2+7ab-2ab^2.=5a^2b+(-3+7)ab+(-4-2)ab^2=5a^2b+4ab-6ab^2
4)4-2xy+7xy-15+xy=-11+6xy