Looking at the "Square of an Odd
" puzzle that asks to prove that the square of an odd number is always 1 more than a multiple of 8, a professor gave this four parts proof: "All odd numbers are of the form 8K+1, 8K+3, 8K+5 or 8K+7. Squaring these numbers produces 8M+1, 8M+9, 8M+25 or 8M+49, which are all of the form 8N+1. QED"
Another professor came by, and gave a single line proof. Can you manage it?
Note: no one who answered the original problem produced either the four parts solution, or the single line one.
(2k+1)^2 = 4k^2 + 4k + 1 = 4k(k+1) + 1 = 8m+1
Posted by Bractals
on 2005-04-19 11:08:36