若25x=1000,40y=1000,则x+y-xy的值为

若25x=1000,40y=1000,则x+y-xy的值为 若(X×X+Y×Y)(X×X+Y×Y-5)=36,则X×X+Y×Y＝ 1000+y=60x 1000-y=40x 若x^2+y^2-6x+8y+25=0 则y/x-x/y的值是 证明：若x>0,y>0,x+y=1,则（x+1/x)(y+1/y)≥25/4 若x^2-y^2=40,(x+y)=8/5,则x-y= 若f(x+y,y/x)=x^2-y^2,则F(X,Y)= 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 y=x+2000 3x-y=1000x 若2.5^x=1000,0.25^y=1000,则1/x-1/y= 若2x=3y,则(x*x+y*y)/x*x=? 若x:y=3则x:(x+y)= 若3x=5y,则x:y=________,(x-y):y=______ 若3x=7y,则y比x= ,x:（x+y）= 若x+y=3 x²-y² 则x-y=?若x+y=3 x²-y²=24 则x-y=? 若x,y,z成等差数列,则(z-x)^2-4(x-y)(y-x)= 比例线段若x+y/x-y=4/3,则x/y=x+y/x-y=4/3,则x/y=要快~~ 若3x-5y=0,则x+y/x=（）,x-y/y=（）,2x-3y/2x+3y=( )