求此双曲线的焦点和焦距y^2/9-x^2/18=1

Question

求此双曲线的焦点和焦距 y^2/9-x^2/18=1

Answer 1

a^2=9 b^2=18 则c^2=a^2+b^2=27 所以c=3倍根号3 因为焦点在Y轴 故焦点为（0,3倍根号3）和（0,-3倍根号3） 焦距等于2c=6倍根号3