How to prove if log is rational/irrational
I'm an English major, now doubling in computer science. The first course I'm taking is Discrete Mathematics for Computer Science, using the MIT 6.042 textbook.
Within the first chapter of the book's practice problems, they ask us multiple times to prove that some log function is either rational or irrational.
Specific cases make more sense than others, but I would really appreciate any advice on how to approach these problems. Not how to carry them out algebraically, but what thought constructs are necessary to consider a log being (ir)rational.
For example, in the case of , proving that is irrational (and therefore , when and is rational) is not an easily solvable problem. I understand the methods of proofs, but the rules of logs are not intuitive to me.
A section from my TF's solution is not something I would know myself to construct:
Since we know that is positive (specifically it is greater than 1), and hence so is . Therefore, we can assume that a and b are two positive integers. Now implies . Thus
Any advice on approaching thought construct to logs would be greatly appreciated!