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17 lines
865 B
17 lines
865 B
2 years ago
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$AF=A'F,ME=EM'$ 所以，问题就变成了求$A'$到$M'$的直线最短距离。
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这里有一个天然的$Rt\triangle A'AM'$
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$OA=3,OM'=OM=3/2$,所以$AM'=9/2$
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下面求$AA'$是多长呢？我们知道$A'$是$A$关于抛物线的对称轴对称的，抛物线的对称轴是$\large x=-\frac{b}{2a}=3$,所以$AA'=6$
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$A'M'=\sqrt{(\frac{9}{2})^2+6^2}=\sqrt{\frac{81+144}{4}}=\frac{15}{2}=7.5$
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#### 扩展阅读
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**[抛物线的对称轴公式](https://iask.sina.com.cn/jxwd/D3oMNMpjIG.html)**
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