Math 5336 Number Theory Dr. Cordero

Class activities for September 9th, 2002

Topics:

Mathematical Induction, II

Divisibility Theory in the Integers, I

**
I.Revisit work from last time**:

**
1.
Hand-out #1 **__ The
Natural Number System__

*
*Problems
1-5.

**
2.
Hand-out #2 **__
Induction and Recursion__

· Discuss the equivalence of the principle of Mathematical Induction and the Well-Ordering Principle.

· Exercises # 3, 5, 6 a, 6c, 12 on p.159-160.

**
3.
Hand-out #3 **__
Mathematical Induction__

Complete the proof on page 10.

**
4.
Additional Practice**

Textbook, Section 1.1, pp.6-7 # 1

**
II. Divisibility**

** **

1. What does it mean for one integer to divide another?

2.
What is the definition of **
even** number? **Odd** number?

3. What can you say about the product of two odd numbers? Two even numbers? An odd and an even number?

4. What can you say about the sum of two odd numbers? Two even numbers? An even and an odd number?

5. Let a, b, d be integers. If d divides a and d divides b, is it necessarily true that d divides ab? What about a+b?

6. What is the converse of each statement in (e)? Is the converse of each statement true?

7. Is it possible to find integers a, b and d such that d divides a+b and d divides a, but d doesn’t divide b?

8. What is the greatest common divisor of two integers a and b?

**9.
**Theorem**: The
division algorithm**

*
Let a and b be integers with b = 0.
Then there are unique integers
q and r such that
0<r<|b| and a=bq+r.*

*
*

Find the unique q and r guaranteed by the Division Algorithm for each pair a and b:

· a=96, b=48

· a=96, b=36

· a=87, b=15

· a=7696, b=4144

10. Applications of the Division Algorithm

·
Use the division
algorithm to show that the square of any **odd **integer n is of the form
8k+1.

· Use the division algorithm to show that for any , the expression is an integer.

11. Additional practice: §2.1 pp 19-20 # 1, 2, 3

**
**