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Pythagorean identities

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Grade 12 Advanced Functions, University Preparation (MHF4U)
B. Trigonometric Functions
22. 12AF.B3.1
22.2 Pythagorean identities

Pythagorean Identities

Sine squared theta plus cosine squared theta equals 1, derived from the Pythagorean theorem, with two related forms.


What You'll Learn

sin squared theta plus cos squared theta equals 1, from the Pythagorean theorem.
Dividing by cos squared theta gives 1 plus tan squared theta equals sec squared theta.
Dividing by sin squared theta gives 1 plus cot squared theta equals csc squared theta.
All three forms describe the same relationship, rearranged.
Use them to substitute and simplify trig expressions.

What You'll Practice

1

Proving Pythagorean identities using the unit circle definition

2

Simplifying expressions with sec²x - 1 and other Pythagorean forms

3

Combining trigonometric fractions with common denominators

4

Multiplying by conjugates to create difference of squares patterns

5

Verifying complex trigonometric identities step-by-step

Why This Matters

Pythagorean identities are essential tools you'll use throughout trigonometry, precalculus, and calculus. They allow you to simplify complex expressions, solve equations, and verify identitiesskills critical for understanding wave functions, circular motion, and advanced calculus techniques like integration.

This Unit Includes

5 Video lessons
Practice exercises
Learning resources

Skills

Pythagorean Identities
Unit Circle
Trigonometry
Identity Proofs
Algebraic Manipulation
Conjugates
Simplification
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