feat(1802): Add R03 materials

input/1802.md

@@ -15,6 +15,7 @@ Most of these materials are side digressions that I typed up.
 They are not considered part of the course,
 and you should not feel obligated to read them; they're just for your interest.
 
+- `R03 2024-09-11` [Main handout for R03](/upload/1802/r03.pdf)
 - `R02 2024-09-09` [Main handout for R02](/upload/1802/r02.pdf)
 - `R02 2024-09-09` [Appendix: proof of dot product property](/upload/1802/dotpf.pdf)
 - `R01 2024-09-04` [Slides from welcome recitation](/upload/1802/welcome-slides.pdf)
@@ -24,6 +25,14 @@ and you should not feel obligated to read them; they're just for your interest.
 
 Source code for these files are posted on [GitHub](https://github.com/vEnhance/1802).
 
+## Answer keys for recitations generated by ChatGPT
+
+Might contain mistakes because it's ChatGPT.
+But probably useful for checking your work.
+If you see a mistake, tell me.
+
+- `R03 2024-09-11` [Answer key for R03](/upload/1802/r03s.pdf)
+
 ## For current students
 
 My recitation is **9:05-9:55am on Mondays and Wednesdays in 2-135**.