Question

已知f(x+y,y/x)=x2-y2求，f(x,y)

Answer 1

• f(x+y,y/x)=x²-y²

  令u=x+y，v=y/x

  则x=u/(v+1)、y=vu/(v+1)

• f(u,v)=u²/(v+1)²-u²v²/(v+1)²

  =u²(1-v²)/(v+1)²

• f(x,y)=x²(1-y²)/(y+1)²