diff --git a/linear-algebra/exercise/6-quadratic-form/quadratic-form.pdf b/linear-algebra/exercise/6-quadratic-form/quadratic-form.pdf
index 9efed3c..efa26c9 100644
Binary files a/linear-algebra/exercise/6-quadratic-form/quadratic-form.pdf and b/linear-algebra/exercise/6-quadratic-form/quadratic-form.pdf differ
diff --git a/linear-algebra/exercise/6-quadratic-form/quadratic-form.tex b/linear-algebra/exercise/6-quadratic-form/quadratic-form.tex
index 13ad7fe..83ea740 100644
--- a/linear-algebra/exercise/6-quadratic-form/quadratic-form.tex
+++ b/linear-algebra/exercise/6-quadratic-form/quadratic-form.tex
@@ -266,6 +266,8 @@ $(x_1,x_2,x_3)^T=\left(\begin{array}{ccc}
 
 由于只有少部分二次型能转换为规范形，所以基本上都是选择题考察。
 
+而且因为规范形的系数必然是0或1或-1，所以不需要求，直接使用惯性定理即可求出。
+
 \subsection{惯性定理}
 
 多用于规范形的判断。