题目先化简,再求值:3x2y+2[2xy2−(xy+12x2y)]−4xy23{x}^{2}y+2[2x{y}^{2}-(xy+\frac{1}{2}{x}^{2}y)]-4x{y}^{2}3x2y+2[2xy2−(xy+21x2y)]−4xy2,其中x=2,y=−12x=2,y=-\frac{1}{2}x=2,y=−21.知识点：整式化简求值章节：数与式 / 整式
