（x+1.8x)*75=1.8xy+1.2xy

（x+1.8x)*75=1.8xy+1.2xy |x|/x+y/|y|+xy/|xy|= (xy)/x 解方程组：x²-xy=0,x²-4xy+4y²=1. 解方程组xy+x=16&xy-x=8 （-3x^y+2xy)-( )=4x^+xy （xy-x的平方）*x-y分之xy= (xy-x平方)乘以x-y份之xy=? 因式分解x^3+2xy-x-xy^2= x³+2xy-x-xy²=（因式分解) (XY-X^2)除以X-Y/XY=? 化简:xy分之3x^2+2xy-xy分之2x^2-xy= 计算：( 根号xy-xy/x+根号xy)÷根号xy-y/x-y= 1.已知x--xy=8,xy--y=--9,求x+y--2xy的值 证明|xy|=|x||y| xy-(x+y)=1000 证明|xy|=|x||y| sin(xy)=x 求dx/dysec(xy)-y ]/x 还是 x/[sec(xy)-y]