Cosine Double Angle Identity
In this tutorial students learn how to verify a trigonometric equation using trigonometric identities like Double Angle and Pythagorean.
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 into what you see below.
(a²  b²) = (a + b) (a  b)
More examples

Trigonometric Identity (Example 2)

Trigonometric Identity (Example 1)

Double Angle Identity (Sine)

Trigonometric Identity (Example 3)

Trigonometric Identity (Example 4)
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