Introduction
The trig rules in IB Math are some of the most widely used formulas across HL and SL courses. They appear in geometry, algebra, vectors, and even calculus problems. Whether solving triangles, proving identities, or modeling real-world applications, knowing the trig rules is essential for success.
The good news is that many of these rules are included in the IB Math booklet. But exam success comes from more than just looking them up—it requires practice, memorization, and knowing when to apply each rule.
Quick Start Checklist
To master the trig rules in IB Math:
- Memorize the sine and cosine rules.
- Review the Pythagorean identities.
- Learn the double-angle and addition formulas.
- Practice applying trig rules to triangles and equations.
- Use RevisionDojo’s guides to prepare for exam-style questions.
Core Trig Rules in IB Math
Here are the essential trig rules every IB student must know:
Sine Rule
a/sin A = b/sin B = c/sin C
Cosine Rule
c² = a² + b² – 2ab cos C
Area of a Triangle
Area = ½ab sin C
Pythagorean Identity
sin²θ + cos²θ = 1
Double-Angle Formulas
- sin(2θ) = 2sinθcosθ
- cos(2θ) = cos²θ – sin²θ
Addition and Subtraction Formulas
- sin(A ± B) = sinAcosB ± cosAsinB
- cos(A ± B) = cosAcosB ∓ sinAsinB
Trig Rules in IB Math Exams
- SL students: Use sine and cosine rules in triangle problems and apply basic identities to simplify expressions.
- HL students: Prove complex trig identities, apply double-angle formulas, and use trig rules in calculus problems.
Example Question
Find the area of a triangle with sides a = 6, b = 8, and angle C = 60°.
Area = ½ab sin C = ½(6)(8)(√3/2) = 12√3 ✅
Common Mistakes with Trig Rules
- Using wrong angles: In the cosine rule, the angle must be opposite the side.
- Forgetting alternate formulas: Like cos(2θ) having three forms.
- Over-relying on calculators: Instead of simplifying with trig rules.
- Mixing radians and degrees: Always check which the exam requires.
Tips for Success
- Memorize the big five: Sine rule, cosine rule, area formula, Pythagorean identity, and double-angle formulas.
- Practice derivations: Helps you remember instead of just memorizing.
- Draw diagrams: Visuals prevent side/angle mislabeling.
- Check exam wording: "Prove" means full working steps are required.
- Use the IB booklet wisely: As a backup, not your first choice.
Frequently Asked Questions (FAQs)
1. Are trig rules in the IB Math booklet?
Yes, most key trig rules are provided, but memorizing them makes exams faster.
2. Do HL and SL students use trig rules differently?
Yes. SL students focus on solving triangles and simplifying, while HL applies rules in calculus and proofs.
3. What’s the most important trig rule to memorize?
The sine and cosine rules—they appear in many exam questions.
4. How do trig rules connect to calculus?
In HL, trig rules simplify integrals and derivatives, e.g., using double-angle formulas.
5. Can I lose marks for not showing trig rule steps?
Yes. IB examiners award method marks, so always write out the substitution.
Conclusion
The trig rules are a cornerstone of IB Math HL and SL. They appear across multiple topics and are essential for solving triangle problems, simplifying equations, and handling calculus applications. By mastering them, students gain speed, accuracy, and confidence in exams.
RevisionDojo helps students build the skills and strategies to apply trig rules effectively and score higher.
RevisionDojo Call to Action
Want to master the trig rules for IB Math? Explore RevisionDojo’s expert resources to strengthen your understanding and exam performance.
