1=x+y 2=20x+30y

先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 已知4x=9y求(1)x+y/y (2)y-x/2x 1/(x+y)-1/(x+y)=3/20 2/(x+y)+3/(x-y)=19/20 这是 集合N=｛（x,y)|（x-1）^2｝+(y-1)^20},M={(x,y)|x^2+y^2 y=(x^2+x)/(x+1) |x|+|y|=30 2|x|-3|y|=20 求x,y 2(x+y) 3x+3y=24 x+y/2x x y/2y= 1