1.2x+5x-3y-6x-2y=7x-6x-5y=x-5y ;
2.-5-x^2+4x+5-3x^2=-4x^2+4x ;
3.x^3+3x^2-5x+6-2x^2+5x-1-x^3-x^2+2=6-1+2=7;
4.=-2a+b-2(-a+b)=-2a+b+2a-2b=-b;
5.=2a+2b-(4a+4b+3a^2+3b^2+2ab)-(5a^2+5b^2+10ab+a+b)
=2a+2b-4a-4b-3a^2-3b^2-2ab-5a^2-5b^2-10ab-a-b=-3a-3b-8a^2-8b^2-12ab
6.-ab-3a^2b+4ab^2+0.5ab-4a^2-3ab^2=0.5ab-3ab^2+4a^2+ab^2
7.=(b^2-3a^b)-(a^3-2a^4)
8.=2x^2+ax-y+6-2bx^2+3x-5y+1=(2-2b)x^2+(a+3)x-4y+5 因为与字母x的取值无关 所以 2-2b=0
a+3=0 b=1 a=-3 3a^2-6ab-3b^2-4a^2-ab-b^2=-a^2-4b^2-7ab=8