这是一个 lead
注意！
\( f(x) = 2 \sin\left( \frac{x}{4} \right) \)
Test!
1 #
\( A(\theta) = 0 \)
2 #
\[ \begin{bmatrix} \dfrac{\partial g_1}{\partial \theta_1} (\theta) \dot{\theta_1} & \cdots & \dfrac{\partial g_1}{\partial \theta_n} (\theta) \dot{\theta_n} \\ & \vdots & \\ \dfrac{\partial g_k}{\partial \theta_1} (\theta) \dot{\theta_1} & \cdots & \dfrac{\partial g_k}{\partial \theta_n} (\theta) \dot{\theta_n} \\ \end{bmatrix} = 0 \]