3x+5y=114x-y=7

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 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 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 （5x+3y)(3y-5x)-(4x-y)(4y+x)= 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 y-x=3 7x+5y=-9 {x+y=5{3x-7y=11 已知x/5=y/3,则(x/x+y)+(y/x-y)-(yxy/xxx-yxy) (7y-3x)-(8y-5x)= {y=x+3,7x+5y+9;