My working: [paste]. Don't
give the answer. Find the
first line where I went
wrong, explain the
misconception behind it, and
let me redo the rest.

Find the Error in My Working

The first wrong line and the misconception behind it — no answer.

Prompt

Here's my attempt at this problem: [paste your working]. Don't give me the answer. Find the first line where I went wrong, explain what misconception produced it, and let me redo the rest myself.