若x-y+2=6/5,则25（y-x-2）=____________要讲出为什么

若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 若x^2+y^2-6x+8y+25=0 则y/x-x/y的值是 若5x+3y=3x+4y=x+2y+6,则x+y=___ 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 若3x-5y=0,则x+y/x=（）,x-y/y=（）,2x-3y/2x+3y=( ) 若f(x+y,y/x)=x^2-y^2,则F(X,Y)= x+y/2+x-y/6=5 2(x+y)-3(x-y)=-2 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 (5)若x/2=y/3(y不为0）则x/y=____,x+y/y=___,y/x-y=___. 若2x-5y=0,则y：x 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y*y)的值 已知X*X+Y*Y+6X-8Y+25=0 求（Y/X)+(X/Y)-2=? 已知x*x+4x+y*y-2y+5=0,则x*x+y*y=? 若2x=3y,则(x*x+y*y)/x*x=? 正整数x,y满足（2x-5)(2y-5)=25,则x+y=? 若X+Y=6,X^2-Y^2=42,则X-Y=?