http://www.mindbites.com/series/294-trigonometry-the-sum-and-difference-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/1236-pre-calculus-using-sum-and-difference-identities Using the sum and difference identities, Professor Burger shows you how to solve a trig function for an unknown angle. For an example, he uses the sin(15 degrees). You can use known angle values for 45 degree and 30 degrees and the formula for the difference of two sines to find the solution. The formula for the difference of two sines is sin(x1 - x2) = sinx1cosx2 - cosx1sinx2. Hence, if you know what the sin and cos values of 30 and 45 degrees are, you should be able to plub them into this formula to arrive at the sine value of 15 degrees. The beauty of the sum and difference formulas for trig functions is that they allow us to decompose a problem we don't know the answer to into component parts to which we do know the answer, thus solving the original problem. Taught by Professor Edward Burger, this lesson was selected from a broader, comprehensive course, Precalculus.
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