1.x^2-3x^2y
2.-1/2a^2bc+1/2cba^2
3.(4a^3b-10b^3)+(-3a^2b^2+10b^3)
4.(4x^y-5xy^2)-(3x^2y-4xy^2)
5.5a^2-{a^2+(5a^2-2a)-2(a^2-3a)}
6.15+3(1-a)-(1-a-a^2)+(1-a+a^2-a^3)
7.(4a^2b-3ab)+(-5a^2b+2ab)
8.(6m^2-4m-3)+(2m^2-4m+1)