(-5x^3-x^2)-(-7x^2+2x^3)化简求值

(-5x^3-x^2)-(-7x^2+2x^3)
=-5x^3-x^2+7x^2-2x^3
=-7x³+6x²-3(2a^2-2ab)+4(a^2+ab-6)-3(2a^2-2ab)+4(a^2+ab-6)=-6a²+6ab+4a²+4ab-24=-2a²+10ab-242m-{n+[am-3(m+2n)]}-5n,其中m=2/3,n=-42m-{n+[am-3(m+2n)]}-5n=2m-n-[am-3m-6n]-5n=2m-6n-am+3m+6n=5m-am=10/3-2a/3