## Homework assignments for Math 28b, Spring 2003

### Problem Set 1. Due Thursday, Jan. 23

- Page 234-237: 3,6, 12,28,40,48
- Show that the only units in
**Z**[i] are 1,i,-1 and -i.
- Find an invertible element in
**Z**[√7] other than 1 or -1. (That's supposed to be the square root of 7 in the brackets.)
- Let B consist of all matrices
where a and b are real numbers. Is B a subring of M
_{2}(**R**)?
Is B a field? Explain.