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Sum and difference identities

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Grade 12 Advanced Functions, University Preparation (MHF4U)
B. Trigonometric Functions
22. 12AF.B3.1
22.3 Sum and difference identities

Sum and Difference Identities

Find the sine, cosine, or tangent of a combined angle like 75 degrees by splitting it into two familiar angles.


What You'll Learn

Sum and difference identities break an angle into two familiar angles, like 75 = 45 + 30.
Sine: sin(a plus or minus b) = sin a cos b plus or minus cos a sin b.
Cosine: cos(a+b) subtracts; cos(a-b) adds cos a cos b and sin a sin b.
Tangent's formula comes from dividing the sine identity by the cosine identity.
These identities are the foundation for the double-angle identities.

What You'll Practice

1

Simplifying expressions using sine and cosine sum and difference identities

2

Evaluating tangent of non-standard angles without a calculator

3

Proving trigonometric identities by expanding sum and difference formulas

4

Finding exact values by converting radians to degrees and applying special triangles

5

Determining trig ratios in different quadrants using reference angles

Why This Matters

Sum and difference identities are essential tools for solving complex trigonometric equations in calculus, physics, and engineering. You'll use these formulas to simplify expressions, prove identities, and evaluate exact valuesskills that appear in standardized tests and advanced STEM courses.

This Unit Includes

8 Video lessons
Practice exercises
Learning resources

Skills

Sum Identities
Difference Identities
Trigonometric Identities
Special Triangles
Reference Angles
Exact Values
Radian Conversion
Identity Proofs
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