問題詳情
已知探照燈內的反射鏡是一個拋物面﹐此曲面由拋物線繞軸旋轉而成﹐因此其縱切面是拋物線的一部分﹒現在有一探照燈的燈口直徑為80公分﹐燈的深度為40公分﹐如右圖所示﹐求此探照燈的焦距為
(E) ﹒
(E) ﹒
參考答案
答案：D
難度：簡單0.77
統計：A(6),B(3),C(7),D(77),E(0)
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