Update complex_integration.html

content/complex_integration.html

@@ -414,7 +414,7 @@ <h2>Properties</h2>
                     \end{eqnarray*}
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                 <p>
-                    In we use the substition $\tau = -t$ in the last integral, then
+                    In we use the substitution $\tau = -t$ in the last integral, then
                 </p>
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                     \begin{eqnarray*}