解7.5x=3.5y 5x+5y=40

解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 x+y=5; x^y+y^x=17 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 Y={X (-5 2x+3y=40x-y=-5 （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 已知x/5=y/3,则(x/x+y)+(y/x-y)-(yxy/xxx-yxy) x-y / 5y= (y-x)^2 / ( ) 已知：4x = 5y,求(x+y) ：y