## Cosine Difference Formula

In this tutorial students learn how to verify a trigonometric equation using trigonometric identities like the difference formula for cosine.

## Virginia Standards of Learning (SOL) **T.5**

## Key Points of Knowledge

### Sum and Difference Formulas

cos (α + β) = cos (α) cos (β) - sin (α) sin (β) cos (α - β) = cos (α) cos (β) + sin (α) sin (β) sin (α + β) = sin (α) cos (β) + cos (α) sin (β) sin (α - β) = sin (α) cos (β) - cos (α) sin (β)

### Pythagorean Theorem

a² + b² = c²

### Pythagorean Triples

3, 4, 5 5, 12, 13 7, 24, 25 etc...

### Quadrants on the Coordinate Plane

I, II, III, IV

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