Geometry & MeasuresTopic Summary
Knowledge Organiser: The Sine Rule
Part of Sine Rule · GCSE GCSE Mathematics revision
This topic summary covers Knowledge Organiser: The Sine Rule within Sine Rule for GCSE Mathematics. Revise Sine Rule in Geometry & Measures for GCSE Mathematics with 12 exam-style questions and 3 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 5 of 5 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 5 of 5
Practice
12 questions
Recall
3 flashcards
Knowledge Organiser: The Sine Rule
Key Terms
- Sine rule: Connects any side with its OPPOSITE angle
- Matched pair: A side and its directly opposite angle (e.g. side a and angle A)
- Non-right-angled triangle: A triangle with no 90° angle
- Ambiguous case: When given ASS (two sides + non-included angle), two triangles may be possible
Must-Know Facts
- Use the sine rule when you have a MATCHED PAIR plus one more piece of information
- Side a is ALWAYS opposite angle A (same letter)
- To find a side: use a/sin A = b/sin B
- To find an angle: flip to sin A/a = sin B/b, then use sin⁻¹
- The three angles of any triangle sum to 180°
Key Formulas
- Find side: a/sin A = b/sin B = c/sin C
- Find angle: sin A/a = sin B/b = sin C/c
- Use when: AAS, ASA (have angle + opposite side)
Common Mistakes
- Wrong pairing: Each side must pair with the angle directly opposite it — a pairs with A, b with B, c with C
- Ambiguous case: When finding an angle with sine rule, there may be two possible answers (acute and obtuse) — check the context
- Using sine rule when cosine rule needed: Sine rule needs an angle-opposite-side pair — use cosine rule for SAS or SSS
- Calculator mode: Must be in degrees mode for GCSE problems