<p><b>「與」符曲線</b>（英語：<span lang="en">Ampersand curve</span>）是二維平面內的一種四次曲線，因形狀酷似「&amp;」號而得名。其曲線方程為：
</p>
<dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \,(y^{2}-x^{2})(x-1)(2x-3)=4(x^{2}+y^{2}-2x)^{2}.}">
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  </semantics></math></span></span></dd></dl><p>所圍成的面積約為<span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle 1.066555\ldots }">
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    <annotation encoding="application/x-tex">{\displaystyle 1.066555\ldots }</annotation>
  </semantics></math></span></span>（OEIS數列A101801）
</p><p>假若在方程右邊加一個足夠小的正常數，則曲線會斷成四個閉合的連通分支，此時曲線在實域上有28條互異的<span data-orig-title="雙切線" data-lang-code="en" data-lang-name="英語" data-foreign-title="bitangent"><span>雙切線</span></span>，是實平面上<span data-orig-title="四次曲線的雙切線" data-lang-code="en" data-lang-name="英語" data-foreign-title="Bitangents of a quartic"><span>四次曲線的雙切線</span></span>數目的最大可能值。
</p>
<h2><span id=".E5.8F.83.E8.80.83.E6.96.87.E7.8D.BB"></span><span id="參考文獻">參考文獻</span></h2>

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**「與」符曲線**（英語：Ampersand curve）是二維平面內的一種四次曲線，因形狀酷似「&」號而得名。其曲線方程為：

　
: $\,(y^{2}-x^{2})(x-1)(2x-3)=4(x^{2}+y^{2}-2x)^{2}.$

所圍成的面積約為 $1.066555\ldots $ （OEIS 數列 A101801）

假若在方程右邊加一個足夠小的正常數，則曲線會斷成四個閉合的連通分支，此時曲線在實域上有 28 條互異的雙切線，是實平面上四次曲線的雙切線數目的最大可能值。

## 參考文獻
&符號曲線