diff --git a/C++/chapTree.tex b/C++/chapTree.tex
index 056d8e02..58bf2013 100644
--- a/C++/chapTree.tex
+++ b/C++/chapTree.tex
@@ -828,10 +828,25 @@ \subsection{Symmetric Tree}
 
 
 \subsubsection{描述}
-Given two binary trees, write a function to check if they are equal or not.
+Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
 
-Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
+For example, this binary tree is symmetric:
+\begin{Code}
+	    1
+	   / \
+	  2   2
+	 / \ / \
+	3  4 4  3
+\end{Code}
 
+But the following is not:
+\begin{Code}
+        1
+       / \
+      2   2
+      \   \
+      3    3
+\end{Code}
 
 \subsubsection{分析}
 无
diff --git a/C++/leetcode-cpp.pdf b/C++/leetcode-cpp.pdf
index 6e3a2430..16f11350 100644
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