Question

cos A.cos (60+A)cos(60-A)=1/4cos3A​

Answer 1

Step-by-step explanation:

tan245°)/ (sin230°+ cos230°) Read more on Sarthaks.com - https://www.sarthaks.com/138612/evaluate-5-cos-260-4-sec-230-tan-245-sin-230-cos-230

Answer 2

Answer:

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Step-by-step explanation:

here ,

cos (60-A) cos (60+A) = cos^2(A)- sin^2 (60)

= cos ^2 (A) - 3/4

now ,

cos A cos (60-A) cos (60+A = cos A ( cos^2 (A) - 3/4)

\ = 1/4 ( 4 cos ^3 (a) - 3 cos A)

{since 4 cos ^3 (a) - 3 cos A = cos 3A }

= 1/4 ( cos 3A)

hence proved