题目化简:(1)y2−2xy−3y2+3xy(1)y^{2}-2xy-3y^{2}+3xy(1)y2−2xy−3y2+3xy；(2)(x2−12+3x)−2(x−x2+1)(2)(x^2-\frac{1}{2}+3x)-2(x-x^2+1)(2)(x2−21+3x)−2(x−x2+1).知识点：整式、整式化简求值章节：第4章 整式的加减 / 4.1 整式
