过双曲线(x^2)-(y^2)=4的焦点且平行于虚轴的弦长是_______

题目

过双曲线(x^2)-(y^2)=4的焦点且平行于虚轴的弦长是_______
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答案

过双曲线(x^2)-(y^2)=4的焦点且平行于虚轴的弦长=2b²/a
双曲线(x^2)-(y^2)=4可化为
x²/4-y²/4=1
a=2,b=2
过双曲线(x^2)-(y^2)=4的焦点且平行于虚轴的弦长=4