# identity prove that cos3x = 4cos^3x-3 cos x

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In this clip you learn how to use the sum and difference identities to find the exact value of trig functions. The ASTC is used to determine the sign of sine cosine tangent cosecant cotangent secant also referred to as function be it positive or negative. The quadrant along with CAST is used for this process. The pythagorean identity will then be used to find all necessary trig functions in order to compute the value of the angles. Additionally the half and double angle identitities will be used to find the trigonometric functions of common angles using the unit circle. In some cases the unit circle the reference angle and the 30-60-90 degrees right triangle and the 45-45-90 right triangles will be used to find the sin cos or tan of common angles. When working with trig functions the angles are expressed using alpha and beta anglular variables and the process is solved step by step clearly showing shortcuts that can be used to solve the problem.

Identify and use reciprocal, identities, quotient identities, pythagorean identities , symmetry identities and opposite angle identites
Use of basic trig identiteis to verify identities find numerical values of trigonometric functions. Solve trig equations and inequalities normal line principal value reduction