diff --git a/content/mathematics/公式大全.md b/content/mathematics/公式大全.md
index 7e6f8c4..d8a0ca0 100644
--- a/content/mathematics/公式大全.md
+++ b/content/mathematics/公式大全.md
@@ -326,6 +326,7 @@ $
 * $A \cdot A* = A* \cdot A = |A| \cdot E$
 * $|A| = \prod_{i=1}^n\lambda_i(\lambda_1,\lambda_2,\cdots,\lambda_n是A的全部特征值)$
 * $|A|\not ={0}\iff A$为可逆矩阵$\iff$A为满秩矩阵，即$r(A) = n$
+* 二维矩阵的伴随矩阵为：主对角线互换，副对角线变号
 
 ---
 ## 矩阵
@@ -900,6 +901,7 @@ $$
   * $A\cong B$则$B \cong A$
   * $A\cong B,B \cong C 则 A\cong C$
   * 同型矩阵A与B等价$\iff r(A)=R(B)$
+  * 矩阵等价问题通常考虑化为阶梯型矩阵后r(A)=R(B)
 
 
 ##### 相似