Question 1010813
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Express cos(90°)- cos(50°) as a product containing only sines and/or cosines
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Use this formula of Trigonometry


{{{cos(alpha) - cos(beta) = -2*sin((alpha+beta)/2)*sin((alpha-beta)/2)}}}


(see the lesson <A HREF=http://www.algebra.com/algebra/homework/Trigonometry-basics/Addition-and-subtraction-of-trigonometric-functions.lesson>Addition and subtraction of trigonometric functions</A> in this site).


When you apply it, you will get


cos(90°)- cos(50°) = -2*sin((140°)/2)*sin((40°)/2) = -2*sin(70°)*sin(20°).