2.已知A=x^3-2xy^2+1,B=x^3+xy^2-3x^2y,求3A-B.
问题描述：
2.已知A=x^3-2xy^2+1,B=x^3+xy^2-3x^2y,求3A-B.
答
合并同类项
3A-B
=3(x^3-2xy^2+1)-(x^3+xy^2-3x^2y)
=3x^3-6xy^2+3-x^3-xy^2+3x^2y
=2x^3-7xy^2+3x^2y+3
答
2x^3-7xy^2+3x^2y+3
就是考查合并同类项，很简单的。
答
A = x^3 - 2 x y^2 + 1
B = x^3 + x y^2 - 3 x^2 y
3 A - B
=3 + 2 x^3 + 3 x^2 y - 7 x y^2
答
3A-B
=3(x^3-2xy^2+1)-(x^3+xy^2-3x^2y)
=3x^3-6xy^2+3-x^3-xy^2+3x^2y
=2x^3-7xy^2+3x^2y+3