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    Trigonometric Identities

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    What are different kinds of trig identities?

    Questions:

    1. If sin x = -1/3, what is cosx?

    2. Simplify the expression (sinx + cosx)^2 + (sinx - cosx)^2

    3. Verify the identity cotx - tanx = (csc2x - sec2x)/sinxcosx

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    https://brainmass.com/math/trigonometry/using-trigonometry-identities-96923

    Solution Preview

    TRIGONOMETRIC IDENTITIES

    Pythagorean Identities

    1. sin2x + cos2x = 1
    2. tan2x + 1 = sec2x
    3. 1 + cot2x = csc2x

    Reciprocal Identities

    1. cscx = 1/sinx
    2. secx = 1/cosx
    3. cotx = 1/tanx

    The Tangent and Cotangent Identities

    1. tanx = sinx/cosx
    2. cotx = cosx/sinx

    Identities for Negatives

    1. sin(-x) = -sinx (the sine function is an odd function)
    2. cos(-x) = cosx (the cosine function is an even ...

    Solution Summary

    This posting lists trigonometric identities and gives examples of different types of problems that make use of them.

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