若函数f(x，y)=ln(x-√x2+y2)(x﹥>y﹥0)，,则f(x+y，x-y)=____．

若函数f(x，y)=ln(x-√x2+y2)(x﹥>y﹥0)，,则f(x+y，x-y)=____．
【正确答案】：f(x+y，x-y)=ln[(x+y)-√((x+y)2-(x-y)2)]=2ln(√x-√y)