[中學] 拋物線正焦弦長
已知拋物線的焦點F在焦弦AB上，若AF=3 BF=6
則拋物線的正焦弦長?
我是想 我先假設一個拋物線y^2=4cx
A(x1,y1) B(x2,y2) F(c,0)
AF=c+x1 BF=c+x2 接著我就不知道該如何解出了@@
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