## Sine Double Angle Identity

In this tutorial students learn how to verify a trigonometric equation. The students will learn to use trigonometric identities like the Double Angle Identity and the Pythagorean Identity.

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

# Key Skills

## Pythagorean Identities

sin²x + cos²x = 1 1 + cot²x = csc²x tan²x + 1 = sec²x

## Trigonometric Identities

1/cos(x) = sec(x) 1/sin(x) = csc(x) tan(x) = sin(x)/cos(x) 1/tan(x) = cos(x)/sin(x) 1/tan(x) = cot(x)

## Sine Double Angle Identity

sin(2x) = 2sin(x)cos(x)

## Cosine Double Angle Identity

cos(2x) = cos²(x) - sin²(x)

## Conjugate

A binomial where the second term is negated.

(x + 2)conjugate(x - 2) (1 - cos x)conjugate(1 + cos x)

## Difference of Perfect Squares

The subtraction of 2 perfect squares can be factored as you see below.

(a² - b²) = (a + b) (a - b)

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