🖍️ RedPen
A real case · you decide
Ellis checks a derivation
Ellis — a first-year engineering student about to hand in a group lab report
A lab partner pasted in a derivation from a homework helper at midnight. It is neat, confident and ends on a clean number. The report is due at nine.
The derivation solves x² = 5x and reports one answer, x = 5. The plot in the report shows the curve crossing zero twice.
Ellis has twenty minutes and a red pen.
The final answer looks plausible. What does Ellis do?
What kind of failure is “divide both sides by x”?
Answers are cheap now. Knowing which line to trust is the part that is still yours.
Before you start
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