一.合并下列同类项1.x^2y-3xy^2+2yx^2-y^2x2.-(5x-y-2z)-3[4x-(x-y-z))+2y]3.2(a+b)^2-(3a+3b)-3(a+b)^2-2(a+b)4.1/9x^n-(4x^n+1)+(x^n+1)-1/2x^n二.求值（先化简,在求值）1/3x^3-2x^2+2/3x^3+3x^2+5x-4x+7
问题描述：
一.合并下列同类项
1.x^2y-3xy^2+2yx^2-y^2x
2.-(5x-y-2z)-3[4x-(x-y-z))+2y]
3.2(a+b)^2-(3a+3b)-3(a+b)^2-2(a+b)
4.1/9x^n-(4x^n+1)+(x^n+1)-1/2x^n
二.求值（先化简,在求值）
1/3x^3-2x^2+2/3x^3+3x^2+5x-4x+7
答
一.合并下列同类项
1.x^2y-3xy^2+2yx^2-y^2x
=(X^2Y+2yx^2)-(3xy^2+xy^2)
=3x^2y-4xy^2
2.-(5x-y-2z)-3[4x-(x-y-z))+2y]
=-5x+y+2z-3[4x-x+y+z+2y]
=-5x+y+2z-9x-9y-3z
=-14x-8y-z
3.2(a+b)^2-(3a+3b)-3(a+b)^2-2(a+b)
=-(a+b)^2-5(a+b)
4.1/9x^n-(4x^n+1)+(x^n+1)-1/2x^n
=[1/9-1/2]x^n-3x^(n+1)
=--7/18x^n-3x^(n+1)
二.求值（先化简,在求值）
1/3x^3-2x^2+2/3x^3+3x^2+5x-4x+7
=x^3+x^2+x+7
把X=?代进去就行了.