Stewart's Theorem in exams

In A-level Maths and Further Maths by Edexcel for 2026, if a question in which Stewart's theorem could be used to save time comes up, can I just state it or do I need to prove it in order to do this?

Reply 1

mqb2766

Original post

by dsvjhshj

In A-level Maths and Further Maths by Edexcel for 2026, if a question in which Stewart's theorem could be used to save time comes up, can I just state it or do I need to prove it in order to do this?

Doubt they would ask a question that would require it. If there was a chunky bit of geometry/trig to do, theyd likely give you some guidance about the approach.

Reply 2

mqb2766

Original post

by dsvjhshj

In A-level Maths and Further Maths by Edexcel for 2026, if a question in which Stewart's theorem could be used to save time comes up, can I just state it or do I need to prove it in order to do this?

Just as an addition to the previous post (for stewarts theorem, and similar ones), its worth looking at stuff like this (if you have the time/inclination) but arguably the main thing is the proof as sometimes (a level) questions are inspired by stuff which is just beyond the curriculum. So for stewart, cos rule twice and eliminate cos(theta) using the basic identity. Its a couple of lines and arguably easier to redo the proof than remember the actual formula itself. I seem to remember a "similar" edexcel gcse question a few years ago which was based on the same triangle splitting, but they wanted you to prove a result based side ratios. It proceeded in a similar way so sin rule on each smaller triangle, then sin(theta) = sin(180-theta), then equate.