diff --git a/docs/10.md b/docs/10.md
index b66c5d373efe814c053f36a31fd9250602844116..b59b4ec0a5a8f5d15ea8f21df58f3365dce03cff 100644
--- a/docs/10.md
+++ b/docs/10.md
@@ -58,13 +58,22 @@ $$
 $$
 
 $$
-= \int \nabla_{theta} \pi _{\theta} (\tau) r(\tau) \text{d} \tau
+= \int \nabla_{\theta} \pi _{\theta} (\tau) r(\tau) \text{d} \tau
 $$
 
 $$
-\int \pi_{\theta}(\tau) \frac{\nabla_{theta} \pi_ {\theta} (\tau)}{\pi_{\theta}(\tau)}r(\tau)\text{d}\tau
+= \int \pi_{\theta}(\tau) \frac{\nabla_{theta} \pi_ {\theta} (\tau)}{\pi_{\theta}(\tau)}r(\tau)\text{d}\tau
 $$
 
 $$
-\mathbb{E}_ {\tau\sim\pi_{\theta}(\tau)}[\nabla_{\theta}\log\pi_{\theta}(\tau)r(\tau)]
+= \mathbb{E}_ {\tau\sim\pi_{\theta}(\tau)}[\nabla_{\theta}\log\pi_{\theta}(\tau)r(\tau)]
+$$
+
+通过对数导数技巧，我们将梯度从期望之外转移到了期望之内。这样做的好处就是，我们不再需要对状态转移函数求梯度，正如下面我们将看到的。
+$$
+\nabla_{theta}J(\theta) = \mathbb{E}_ {\tau\sim\pi_{\theta}(\tau)}[\nabla_{\theta}\log\pi_{\theta}(\tau)r(\tau)]
+$$
+
+$$
+= \mathbb{E}_ {\tau\sim\pi_{\theta}(\tau)}[\nabla_{theta} [\logP(s_1)+\sum_{t=1}^{T}(\log\pi_{\theta}(a_t|s_t) + \log P(s_{t+1}|s_t,a_t))]r(\tau)]
 $$
\ No newline at end of file