Saurav B.

asked • 08/08/14

cos(A+B)=cosA.cosB - sinA.sinB

How this formula is derived 

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Philip P. answered • 08/09/14

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It's difficult to show without graphics - try the website below:
 
http://www.trans4mind.com/personal_development/mathematics/trigonometry/compoundAngleProofs.htm
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Francisco E.

I Agree with Philip, I do not know how to copy and paste a graph in this system, also the formula derivation without graph may be time consuming and messy.
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08/09/14

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