## At A Glance

### Pre-Calculus: Using Double-Angle Identities

http://www.mindbites.com/series/295-trigonometry-double-angle-identities for a bundle of videos on . For an even broader bundle of videos that cover and , check out http://www.mindbites.com/series/289-trigonometry-trigonometric-identities . To search for topic-specific help in our library of 400+ video products for Trigonometry & Pre-Calculus, please refer to our Trigonometry category at: http://www.mindbites.com/category/31-trigonometry and our Calculus Category at http://www.mindbites.com/category/23-calculus . To check out our full Trig & Pre-Cal video course, with 150 videos included, refer to: http://www.mindbites.com/series/845-trigonometry-full-course . Or, for access to this single video, go to: http://www.mindbites.com/lesson/1235-pre-calculus-using-double-angle-identities Double-angle identities allow you to simplify trigonometric equations with a 2 as the coefficient. (similar formulae exist for trig functions with 1/2 or 3 as the coefficient). In this lesson, Professor Burger uses the equation cos2x = sinx as an example. If this equation were simply cos x = sinx, we could divide to re-write the formula as sinx/cosx = tan x = 0, but in this case, we have a coefficient in advance of one of the arguments, which is why we need to use the double-angle formulas. After using the double-angle formulas in the provided example to simplify, you can further simplify these equations using trig identities (like the Pythagorean identity) and factoring. These tools will help you to solve many trig equations. The duble angle identities for sine, cosine, tangent and cotangent are: sin2x = 2sinxcosx, cos2x = cos^2x-sin^2x, tan 2x = 2tanx/(1-tan^2x), and cot2x = (cot^2x-1)/2cotx. Taught by Professor Edward Burger, this lesson was selected from a broader, comprehensive course, Precalculus.
Length: 02:49

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