（x+1.8x)*75=1.8xy+1.2xy

化简:xy分之3x^2+2xy-xy分之2x^2-xy= 解方程组xy+x=16&xy-x=8 （-3x^y+2xy)-( )=4x^+xy （xy-x^2)乘以(xy)/(x-y) 计算：(xy-x²)×x-y/xy 由已知x+y=-2,xy=3那么2(x+xy)-[(xy-3y)-x]-(-xy)等于多少? 先化简,再求值 ⒈2(Xy+Xy)-3(Xy-xy)-4Xy,其中X=1,y=-1 已知x-xy=8,xy-y=-9,求x+y-2xy的值 若x＞1，y＞0且满足xy=xy，xy＝x 已知x:y=3:2,求(x²+3xy)/(xy+2xy) 已知x-y=4xy，则2x+3xy-2yx-2xy-y 多元函数极限lim sin(xy)/x (x.y) -> (0.2) = lim {[sin(xy) / xy ] *