This video is about the cosine rule for GCSE maths, and is aimed at around grade 7+. It’s fairly tough and please do
– stop the video
– work through the question
– compare your solution
I hope the video helps and please leave a comment – thanks!
Download a copy of the question here:
QT Tough Questions – Proving Cosine
Here’s a copy of the written answer:
QT Tough Questions – Proving Cosine ANSWERS
The question uses the Cosine Rule, but you are asked to prove within a parallelogram. The key is to notice that AC = PQ at the bottom of each triangle. Both of these are exactly the same (a), so the expressions are then equal to each other.
These problems are fairly infrequent for GCSE maths, although they tend to be high marks, and encourage you to really demonstrate your knowledge and confidence.
Top Tips!
- Always work methodically and show your working
- Check your calculations
- Is it a reasonable answer?
Here’s other posts that also might be of interest:
Using the Cosine Rule; Grade 6 Maths GCSE Non-Calculator
The cosine rule; GCSE maths grade 6+
Parallel or perpendicular lines on a graph; mid-level questions
Edexcel GCSE Maths June 2018 Paper 1
Edexcel Maths Higher Paper 2 November 2018
AQA GCSE Maths Higher 2018; Paper 1
Edexcel GCSE Maths Foundation Paper 2017; Paper 3
Edexcel GCSE maths foundation November 2018 paper 2
Speed Distance Time; mid level GCSE mathematics questions
Please do leave a comment below if you are not sure. Alternately you can view my YouTube channel and leave a comment there – I’ll always try to respond as quickly as possible.
Watch on YouTube:
Cosine Rule – Another Tough Question
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