题目化简:(1)−a+2a−3a(1)-a+2a-3a(1)−a+2a−3a；(2)x2+5y−4x2−3y−1(2)x^{2}+5y-4x^{2}-3y-1(2)x2+5y−4x2−3y−1；(3)32x+2(x−13y2)−(32x+13y2)(3)\frac{3}{2}x+2(x-\frac{1}{3}{y}^{2})-(\frac{3}{2}x+\frac{1}{3}{y}^{2})(3)23x+2(x−31y2)−(23x+31y2)；(4)−2y3+(3xy2−x2y)−2(xy2−y3)(4)-2y^{3}+(3xy^{2}-x^{2}y)-2(xy^{2}-y^{3})(4)−2y3+(3xy2−x2y)−2(xy2−y3).知识点：解二元一次方程组——代入消元法章节：方程与不等式 / 二元一次方程组
