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	<title>Function real-differentiable at a point - Revision history</title>
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	<updated>2026-05-11T10:39:53Z</updated>
	<subtitle>Revision history for this page on the wiki</subtitle>
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	<entry>
		<id>https://companal.subwiki.org/w/index.php?title=Function_real-differentiable_at_a_point&amp;diff=176&amp;oldid=prev</id>
		<title>Vipul: 1 revision</title>
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		<updated>2008-05-18T19:12:47Z</updated>

		<summary type="html">&lt;p&gt;1 revision&lt;/p&gt;
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				&lt;td colspan=&quot;1&quot; style=&quot;background-color: #fff; color: #202122; text-align: center;&quot;&gt;← Older revision&lt;/td&gt;
				&lt;td colspan=&quot;1&quot; style=&quot;background-color: #fff; color: #202122; text-align: center;&quot;&gt;Revision as of 19:12, 18 May 2008&lt;/td&gt;
				&lt;/tr&gt;&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-notice&quot; lang=&quot;en&quot;&gt;&lt;div class=&quot;mw-diff-empty&quot;&gt;(No difference)&lt;/div&gt;
&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;</summary>
		<author><name>Vipul</name></author>
	</entry>
	<entry>
		<id>https://companal.subwiki.org/w/index.php?title=Function_real-differentiable_at_a_point&amp;diff=175&amp;oldid=prev</id>
		<title>Vipul: New page: ==Definition==  ===For an open subset of the complex numbers===  Suppose &lt;math&gt;U&lt;/math&gt; is an open subset of &lt;math&gt;\mathbb{C}&lt;/math&gt;, and &lt;math&gt;f:U \to \mathbb{C}&lt;/math&gt; is a function. Let...</title>
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		<updated>2008-04-18T20:14:53Z</updated>

		<summary type="html">&lt;p&gt;New page: ==Definition==  ===For an open subset of the complex numbers===  Suppose &amp;lt;math&amp;gt;U&amp;lt;/math&amp;gt; is an open subset of &amp;lt;math&amp;gt;\mathbb{C}&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;f:U \to \mathbb{C}&amp;lt;/math&amp;gt; is a function. Let...&lt;/p&gt;
&lt;p&gt;&lt;b&gt;New page&lt;/b&gt;&lt;/p&gt;&lt;div&gt;==Definition==&lt;br /&gt;
&lt;br /&gt;
===For an open subset of the complex numbers===&lt;br /&gt;
&lt;br /&gt;
Suppose &amp;lt;math&amp;gt;U&amp;lt;/math&amp;gt; is an open subset of &amp;lt;math&amp;gt;\mathbb{C}&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;f:U \to \mathbb{C}&amp;lt;/math&amp;gt; is a function. Let &amp;lt;math&amp;gt;z_0 \in U&amp;lt;/math&amp;gt; be a point. We say that &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is &amp;#039;&amp;#039;&amp;#039;real-differentiable&amp;#039;&amp;#039;&amp;#039; at &amp;lt;math&amp;gt;z_0&amp;lt;/math&amp;gt; if there exists a matrix &amp;lt;math&amp;gt;(Df) \in M_2(\R)&amp;lt;/math&amp;gt; such that:&lt;br /&gt;
&lt;br /&gt;
&amp;lt;math&amp;gt;\lim_{h \to 0} \frac{f(z + h) - f(z) - (Df)(h)}{\| h \|} = 0&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
Here &amp;lt;math&amp;gt;(Df)(h)&amp;lt;/math&amp;gt; denotes &amp;lt;math&amp;gt;Df&amp;lt;/math&amp;gt; multiplied with &amp;lt;math&amp;gt;h&amp;lt;/math&amp;gt; as a column vector.&lt;br /&gt;
&lt;br /&gt;
Such a &amp;lt;math&amp;gt;Df&amp;lt;/math&amp;gt; is termed a real differential of &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt;.&lt;/div&gt;</summary>
		<author><name>Vipul</name></author>
	</entry>
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