IDENTITIESIDENTITIES
IDENTITIES
THE MORE IMPORTANT
De ning relations for tangent, cotangent, The Pythagorean formula for sines
secant, and cosecant in terms of sine and and cosines. This is probably the most
cosine. important trig identity.
Identities expressing trig functions in Periodicity of trig functions. Sine,
terms of their complements. There's not cosine, secant, and cosecant have period
much to these. Each of the six trig 2π while tangent and cotangent have
functions is equal to its co-function period π.
evaluated at the complementary angle.
Identities for negative angles. Sine, Ptolemy’s identities, the sum and
tangent, cotangent, and cosecant are odd difference formulas for sine and
functions while cosine and secant are cosine.
even functions.
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