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If sin 2a + sin 2b = 1/2 and cos 2a + cos2b = 3/2, then cos^2(a-b) is equal to (A) 3/8 (B) 5/8 [correct answer] (C) ¾ (D) 5/4 Please give the solution for this question..

If sin 2a + sin 2b = 1/2 and cos 2a + cos2b = 3/2, then cos^2(a-b) is equal to
(A) 3/8
(B) 5/8 [correct answer]
(C) ¾
(D) 5/4
 
Please give the solution for this question..

Grade:

3 Answers

Saurabh Koranglekar
askIITians Faculty 10335 Points
5 years ago
Dear Anushka Khuspe



576-1636_1.jpg

Answer is C

please find attached file

also please revert for this or similar problems

Thanks and regards
Anushka Khuspe
8 Points
5 years ago
Thank you for your attempt to this question. It really helped me. 
The only thing is, the rest of the solution is correct but I think that you have done some mistake in the last line of the solution (regarding the identity of trigonometry used) and by correcting that error I get the answer as 5/8...which is probably the correct answer. 
Saurabh Koranglekar
askIITians Faculty 10335 Points
5 years ago
cos(2(a-b)) = ¼ and not ½

you are correct

thanks and keep posting

good luck,576-914_1.JPG

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