19/08/2026
Here’s a mistake that costs a full question — and why we think it matters more than it looks.
(3x − 5)² = 9x² − 25.
It’s wrong. Squaring a binomial means squaring both terms and the middle term you get from multiplying them together. Skip that, and the whole answer changes.
What’s interesting is who makes this mistake. It’s rarely the learners who haven’t studied — it’s usually the diligent ones, who memorised a rule without ever being shown why it works. The rule holds up fine until a question is built specifically to expose the gap. Then it quietly costs marks, in a way that looks like carelessness but isn’t.
Swipe for the full correction, done properly with a full expansion and the quadratic formula.
You can’t fix a gap you haven’t found — and gaps like this one are invisible until a test is built to catch them.
oddclasses.co.za
