I have problems understanding proofs by contradiction.
This is one of my exercises :
Give a proof by contradiction that if 2n^9 + 5n^7 - 6n^4 - n^2 - 27 = 0 where n is an integer, then n is a positive integer (n > 0)
Obviously, I have to assume that n is negative integer. What I don't know is how to proceed with the contradiction. I try to substitute n in the equation with different positive and negative integers, but it is never equal to zero
Thank you in advance for your answers.