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## The long way round

Today one of my Y12s was looking through a C3 paper he found on my desk. (For those unaware A level maths, studied in Y12 and Y13, ie from 16-18, is currently modular. There are 4 Core Pure modules known as C1, C2, C3 and C4. The first two are studied in Y12 and the second two in Y13.) He came across this question:

While looking at it he said, “are you sure this is a C3 question?” I told him it was and he then said “But I can answer it.”

I looked at the question, all the main skills it tests are taught at C1 and C2, but the chain rule for differentiation isn’t taught til C3. I thought about it and realised that yes, with the application of the binomial expansion (a C2 skill), or indeed a long winded brackets expansion, it would give him a polynomial he could differentiate.

Then it occurred to me that it was in fact a brilliant question to set my Y12s as revision. It allows them to see links between the things they’ve learned, allows them to practice important skills from C1 and C2, namely the differentiation, the coordinate geometry involved finding te equation of a tangent and the binomial expansion, and to solve a problem using those skills.

It took them longer than it would have taken someone who knew about the chain rule, but it was time we’ll spent and I got some perfect answers from them. I didn’t tell any of them how to do it, they managed to talk each other through it, and I only had to pick up on one slight error when one of them had a slight hiccup with a power. I think I need to have a good look through some more higher level papers to see if I can find any other gens to test the earlier skills.

This post has been cross-posted to Betterqs here.