Question

cos2A=2cos^2A-1 prove that
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Answer 1

Step-by-step explanation:

cos 2A = cos(A+A)

= (cos A)(cos A) - (sin A)(sin A)

= cos^2 A - sin^2 A

= cos^2 A- (1-cos^2 A)

= 2cos^2 A - 1

•

• • 【 cos(a+b) =(cosa)(cos b) - (sin a)(sin b)】

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