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20-Knowledge/Synthesized-Japanese-Class-Notes.md

@@ -205,6 +205,13 @@ You can express potential without conjugating the verb into its unique form by u
     - **Past Tense + とき**: The main action occurs *after* the action in the とき clause was completed.
         - *Example: パリに行った時にこのかばんを買いました。 (When I went to Paris, I bought this bag.)*
 
+- **Expressing Apology (〜てすみませんでした)**: Used to apologize for an action, often for something that couldn't be done.
+    - **Formula**: Verb (て-form) + すみませんでした
+    - **Note**: If apologizing for *not* doing something, use the negative て-form (なくて).
+    - *Example*: パーティーへ行かなくて、すみませんでした (I'm sorry I couldn't go to the party.)
+    - *Example*: 本をなくして、すみませんでした (I'm sorry for losing the book.)
+    - *Example*: 宿題を持って来なくて、すみませんでした (I'm sorry for not bringing the homework.)
+
 ## Vocabulary
 
 ### Nouns
@@ -277,6 +284,8 @@ You can express potential without conjugating the verb into its unique form by u
 - **ただいま** - I'm home
 
 - **おかえり** - Welcome back
+- **行ってきます (いってきます)** - I'm leaving
+- **お帰りなさい (おかえりなさい)** - Welcome Back (more formal)
 
 - **いただきます** - Said before eating