diff --git a/03-UnrealEngine/Math/四元数学习笔记.md b/03-UnrealEngine/Math/四元数学习笔记.md
index b3d7e6d..a332e26 100644
--- a/03-UnrealEngine/Math/四元数学习笔记.md
+++ b/03-UnrealEngine/Math/四元数学习笔记.md
@@ -60,6 +60,23 @@ $$p \rightarrow q\cdot p \cdot q^-1$$
 
 ## 四元数规范化
 $$x^2 + y^2 + z^2 =1$$
+
+## 四元数求反
+```c++
+inline QQuaternion QQuaternion::inverted() const
+{
+    // Need some extra precision if the length is very small.
+    double len = double(wp) * double(wp) +
+                 double(xp) * double(xp) +
+                 double(yp) * double(yp) +
+                 double(zp) * double(zp);
+    if (!qFuzzyIsNull(len))
+        return QQuaternion(float(double(wp) / len), float(double(-xp) / len),
+                           float(double(-yp) / len), float(double(-zp) / len));
+    return QQuaternion(0.0f, 0.0f, 0.0f, 0.0f);
+}
+```
+
 # FBX
 四元数旋转顺序 xyz
 可以使用