This is a free lesson from our course in Trigonometry

 This lesson introduces and walks you through the Trigonometric Identities. You'll learn it with the help of some examples, practice questions with solution, and watching video as well as explanations by the instructor in their hand writing. The trigonometric identities are equalities that involve trigonometric functions that are true for every single value of the occurring variables.Here you'll learn how these identities are useful when expressions involving trigonometric functions need to be simplified and put into application. (More text below video...)
Other useful lessons:
 Pythagorean Trigonometric Identity Verifying Trigonometric Identities
(Continued from above) Some of the important trigonometric identities are:
Reciprocal Identities:
csc  = 1/sin                sin  = 1/csc
sec = 1/cos               cos = 1/sec
tan = 1/cot               cot = 1/tan

Tangent and Cotangent Identities:
tan  =  sin /cos
cot  =  cos /sin

Pythagorean Identities:
sin2  + cos2  = 1
tan2  + 1 = sec2
1 + cot2  = csc2

Even/Odd Identities
sin (- ) = - sin
cos(- ) = cos
tan (- ) = - tan

Sum and Difference Identities
Sin(A-B) = sin A cos B – cos A sin B
Cos(A-B)= cos A cos B + sin A Sin B

Double Angle Identities
Sin2 = 2 sin cos
cos 2 = cos2 – sin2 = 2cos2 -1=1- 2 sin2
tan2 = 2tan/1-tan2
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