设p(x,y),由曲线上动点P到F1、F2的距离之差为6则|√[(x+4)^2+y^2]|-|√[(x-4)^2+y^2]|=6化简得x^2/9-y^2/7=1
双曲线由定义知道c=4,2a=6,a=3,b^2=c^2-a^2=7x^2/9-y^2/7=1
