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What is the formula for cos3a.and also tell about the method to get it

What is the formula for cos3a.and also tell about the method to get it

Grade:9

1 Answers

Nikhil Upadhyay
171 Points
8 years ago
cos3a=4cos3a-3cosa.you can get it by writing it in the form cos(a+b) as cos(2a+a)
=cos2a*cosa-sin2a*sina
=(2cos2a-1)cosa-2sinacosasina
=(2cos2a-1)cosa-2cosa(1-sin2a)
=2cos3a-cosa-2cosa+2cos3a
=4cos3a-3cosa.PLZ approve

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