Worked Example: Finding a Side
Part of Cosine Rule · GCSE GCSE Mathematics revision
This study notes covers Worked Example: Finding a Side within Cosine Rule for GCSE Mathematics. Revise Cosine Rule in Geometry & Measures for GCSE Mathematics with 12 exam-style questions and 3 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 4 of 5 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 5
Practice
12 questions
Recall
3 flashcards
Worked Example: Finding a Side
Find side a when b = 7cm, c = 9cm, and A = 60°.
Solution
a² = b² + c² - 2bc cos A
a² = 49 + 81 - 2(7)(9)cos 60°
a² = 130 - 126(0.5) = 130 - 63 = 67
a = √67 = 8.2 cm (1 d.p.)
Keep building this topic
Read this section alongside the surrounding pages in Cosine Rule. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Cosine Rule
Which formula is the cosine rule for finding side a?
Show that when angle A = 90°, the cosine rule reduces to Pythagoras' theorem.
Quick Recall Flashcards
12 questions on Cosine Rule — practise free
Instant marking, adaptive difficulty, and 3 spaced repetition flashcards. Free until your GCSEs.
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