x+y=400 15%x+80%y=125 二元一次方程解(加减法)急!

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 化简 x / y(x+y) - y / x(x+y) = (x*x+y*y)(x*x+y*y)-(x*x+y*y)=12 求x*x+y*y等于多少 (12-x)*y+x*2=26 (15-x)*y+y*2=35(12-x)*y+x*2=26 (15-x)*y+y*2=35 x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空 x.y都是自然数,且x(x-u)-y(y-x)+12,求x.y得值快1且x(x-y)-y(y-x)=12 x+80%y=42 y-x=12 12x+20y=20x+15y [(y*y*y-y)/(xy+1)*(xy+1)-(x+y)*(x+y)]/[(x+y)*y/(x+1)]其中x=-11,y=1/12,化简再求值. x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x=15y x^2+xy=12,xy+y^2=15,求(x+y)^2-(x+y)(x-y) y=x(x (X,Y) f(x,y)={12y^2,0 12y(x-y)^2-8(x-y)^3=? 已知|x|+x+y=10 |y|+x-y=12 求 x+y=? 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15