# THE FIRST MIDTERM EXAMINATION .

```THE FIRST MIDTERM EXAMINATION
WILL BE IN CLASS ON THURSDAY, AUGUST 14
.
It will cover the material through Homework IV.
Mathematics 109
August 11, 2008
SAMPLE FIRST MIDTERM EXAMINATION
Use no notes or books. Use no calculators or other electronic devices. Consult no one
other than the Teaching Assistant or the Instructor. Write clear, careful solutions. Do all
1. The following statements have the set of positive real numbers as their set of
meanings. In each case, first write the statement without logic symbols and second either
prove the statement or give a counterexample.
(a) x yxy  1
(b) x yxy  1
2. This problem builds up to showing that there is no rational number whose cube is 2.
(a) Show that if 2 divides n , then 8 divides n 3 .
(b) Show that if 2 divides n 3 , then 2 divides n .
(c) Show that there is no rational number whose cube is 2 .
3. For each part of the previous problem, indicate the method of proof used.
4. Consider sets A and B . Prove that A  B  A if and only if B  A .
5. Prove that if each of x , y and z is a real number, then x 2  y 2  z2  xy  xz  yz .
```