帮我看看几道数学题!

(2xy-y)-(-y+yx)
=2xy-y+y-yx
=xy
5(a平方b-3ab平方)-2(a平方b-7ab平方)
=5a^2b-15ab^2-2a^2b+14ab^2
=3a^2b-ab^2
(4a+3a平方-3+3a立方)-(-a+4a立方)
=4a+3a^2-3+3a^3+a-4a^3
=-a^3+3a^2+5a-3
a=-2所以原式=(-2)^3+3*(-2)^2+5*(-2)-3
=-8+12-10-3
=-9
2x平方y-2xy平方-〔(-3x平方y平方+3x平方y)+(3x平方y平方-3xy平方)〕
=2x^2y-2xy^2-(-3x^2y^2+3x^y+3x^2y^2-3xy^2)
=2x^2y-2xy^2-(3x^2y-3xy^2)
=2x^2y-2xy^2-3x^2y+3xy^2
=-x^2y+xy^2
=xy(y-x)
x=-1,y=2所以原式=(-1)*2*[2-(-1)]
=-6