Videos and lessons with examples and solutions to help High School
Algebra 2 students learn about trigonometric identities.

Trigonometric Identities:

Identities are equations true for any value of the variable.

Since a right triangle drawn in the unit circle has a hypotenuse of length 1, we define the trigonometric identities x = cos(theta) and y = sin(theta).

In the same triangle, tan(theta)=x/y, so substituting we get tan(theta) = sin(theta)/cos(theta), the tangent identity.

Another key trigonometric identity sin^{2}(theta) + cos^{2}(theta) = 1 comes from using the unit circle and the Pythagorean Theorem.

Trigonometric Identities: How to Derive / Remember Them - Part 1 of 3.
Trigonometric Identities: How to Derive / Remember Them - Part 2 of 3.

Trigonometric Identities: How to Derive / Remember Them - Part 3 of 3.
Fundamental Trigonometric Identities

The reciprocal identities, quotient identities and the Pythagorean identities.

Trigonometric Identities
Deriving Trigonometric Identities from 3 Known Identities

You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

Identities are equations true for any value of the variable.

Since a right triangle drawn in the unit circle has a hypotenuse of length 1, we define the trigonometric identities x = cos(theta) and y = sin(theta).

In the same triangle, tan(theta)=x/y, so substituting we get tan(theta) = sin(theta)/cos(theta), the tangent identity.

Another key trigonometric identity sin

Trigonometric Identities: How to Derive / Remember Them - Part 1 of 3.

The reciprocal identities, quotient identities and the Pythagorean identities.

Trigonometric Identities

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You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

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