minor changes

Author: longfei-chen

chp07/subsections/7.11.html

@@ -535,9 +535,9 @@ <h2>7.11.2 微分方程类型总结表</h2>
                         </tr>
                         <tr>
                             <td><strong><a href="7.9.html">欧拉方程</a></strong></td>
-                            <td>$$x^2y'' + pxy' + qy = 0$$</td>
+                            <td>$$x^2y'' + pxy' + qy = f(x)$$</td>
                             <td>换元法</td>
-                            <td>设 $x = e^t$<br>$\frac{d^2y}{dt^2} + (p-1)\frac{dy}{dt} + qy = 0$</td>
+                            <td>设 $x = e^t$<br>$\frac{d^2y}{dt^2} + (p-1)\frac{dy}{dt} + qy = f(t)$</td>
                             <td>$$x > 0$$</td>
                         </tr>
                     </tbody>