M201: First graded homework
For each question, state the proposition and write a formal proof.

(3 points.)
If x is an integer,
then x^{2} + 5x +6 is even.

(3 points.)
If x is an integer,
and x^{2} + 4 is odd,
then x is odd.

(3 points.)
There are no integers x, y
such that 6x + 9y = 1.
