Prove the following statements. Use only definitions from Chapter 4 and the assumptions shown below.
1. For all integers a, b, and c, if a | b and a | c then a | (2b - 3c).
2. If a is any odd integer, then a^2 + a is even.
3. For any rational numbers r and s, 2r + 3s is rational.
Assumptions:
In this text, we assume a familiarity with the laws of basic algebra, listed in Appendix A.
We also use the three properties of equality: For all objects A, B, and C,
i) A = A
ii) if A = B then B = A, and
iii) if A = B and B = C, then A = C.
We also use the substitution property – for all objects A and B, if A = B, then we may substitute B wherever we have A.
We assume that there is no integer between 0 and 1 and that the set of all integers is closed under addition, subtraction, and multiplication. This means that sums, differences, and products of integers are integers.