x+y=22 2.5x+7y=100

X+Y=7(100X+Y)-(10Y+X)=(10Y+X)-(10X+Y) 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 {5x-2y=7y+2x 3x+2y=22 若x+7y=y-3x，求x 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013 ) y=cos(x-y) x+y=5; x^y+y^x=17 因式分解下列式子：x(x-y)+y(y-x)=? 若3x=7y,则y分之x= ,x:（x:y）= 若3x=7y,则y比x= ,x:（x+y）=