1. C is the midpt. of AB
1. given
2. AB = 10
2. given
3. AC = CB
3. def. of midpt.
4. AC + CB = AB
4. seg. add. post.
5. AC + CB = 10
5. subst. prop.
6. AC + AC = 10
6. subst. prop.
7. 2AC = 10
7. add
8. AC = 5
8. div. prop.