The following is a list of useful Trigonometric identities: Quotient Identities, Reciprocal Identities, Pythagorean Identities, Co-function Identities, Addition Formulas, Subtraction Formulas, Double Angle Formulas, Even Odd Identities, Sum-to-product formulas, Product-to-sum formulas.
We will also learn how the different Trigonometric identities are derived and how they may be used.
Related Topics: More Lessons on Trigonometry
sin (a + b) = sin a cos b + cos a sin b
cos (a + b) = cos a cos b – sin a sin b
sin (a - b) = sin a cos b - cos a sin b
cos (a - b) = cos a cos b + sin a sin b
sin 2a = 2 sin a cos a
cos 2a = cos 2a – sin 2a = 2 cos2a – 1 = 1 – 2 sin2a
This video shows how to derive the Quotient, Reciprocal and Pythagorean identities.
How to use the double-angle identities to determine function values.
The derivations of the half-angle identities for both sine and cosine, plus listing the tangent ones. Then a couple of examples using the identities.
How to use the half-angle identities to determine function values.
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