Question

已知X、Y满足X平方+Y平方+1.25=2X+Y,求代数式XY/X+Y

Answer 1

x^2+y^2+1.25=2x+y

x^2-2x+1+y^2-y+0.25=0

(x-1)^2+(y-0.5)^2=0

x=1,y=0.5.

xy/(x+y)=1*0.5/(1+0.5)=0.5/1.5=1/3