Fix Typos in lecture 9

[yurm04]

Description

What needs to be fixed/addressed/accomplished/discussed in this issue.
There are several typos in lecture 9 notes, go through through and correct them. Make sure to use proper Markdown

Checklist

• Title is short, sweet, to the point.
• Issue is descriptive enough for anyone to come across it and know exactly what is being presented.
• The correct labels have been added.
• The expected behavior is described (if applicable).
• Steps to reproduce the problem have been included (if applicable).
• Screenshots were included (if applicable).

Mentions

Include anyone that should be mentioned in this issue
@yurm04