②×2得4f（x）十2f（1／x）＝6／x②－①得3f（x）＝6／x－3x③③除以3得f（x）＝3／x－x
2根号2+3=2+2根号2+1=根号2方+2根号2+1=（根号2+1）方
你用2*②-①，消去f（1/x）啊
