TMUA-P2-PRF2-008 — Paper P2 · Proof by cases · Level 1

Options

1. A
   Assume $n$ is even only.
2. B
   If $n=2k$ then $n^2+n=2(2k^2+k)$ is even; if $n=2k+1$ then $n^2+n=2(2k^2+3k+1)$ is even. Both cases give even.
3. C
   Check $n=2$ only.
4. D
   $n^2$ and $n$ are separately always even.

Letters only — the answer key is hidden. Work it out, then check the solution below.

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