How to Use the Sine Rule in Non-Right-Angled Triangles

Learn how to use the sine rule to find missing sides and angles in any triangle — step-by-step. The sine rule works on triangles without a right angle, which is exactly where SOHCAHTOA stops working. The sine rule: a / sin A = b / sin B = c / sin C Side a is opposite angle A, side b is opposite angle B, side c is opposite angle C. To find a side, use the rule with sides on top. To find an angle, flip it so the sines are on top — then use the inverse sine button on your calculator to get the angle. Perfect for Year 10 and Year 11 students learning trigonometry, anyone revising for a maths exam, or learners who need a clear walkthrough with no skipped steps. 📘 What you'll learn: When to use the sine rule (and why SOHCAHTOA isn't enough) The angle-side labelling convention: lowercase a opposite capital A The sine rule formula and how to read it When to use the rule the right way up vs flipped upside down How to substitute, rearrange, and calculate to find a missing side How to use the inverse sine button (sin⁻¹) to find a missing angle Why you only ever use two ratios at a time ⏱️ Timestamps: 00:00 The Sine Rule 01:30 Example 1 — finding a side 04:20 Example 2 — finding a side 07:00 Example 3 — finding an angle 11:20 Final example — finding an angle 🎯 Who this is for: Year 10 and Year 11 students learning trigonometry, GCSE and IGCSE students revising for exams, learners who already know SOHCAHTOA and need the next tool, and anyone who wants a clear tutorial that shows every step. 📚 Helpful to watch first: Pythagoras' Theorem SOHCAHTOA — Finding Missing Sides with Trigonometry 📺 Coming next: The cosine rule — the other big formula for non-right-angled triangles, used when the sine rule doesn't fit your information. 🔗 Find more maths lessons and tutoring resources: https://tutor-marketplace.com If this video helped, please like and subscribe for more step-by-step maths tutorials. #SineRule #Trigonometry #Trig #NonRightAngledTriangles #Year10Maths #Year11Maths #MathsTutorial #GCSEMaths #MathHelp #Mathematics