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Trignometry

Blazing goIITian

Joined:	12 Apr 2008
Post:	2717

25 May 2009 09:36:07 IST

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407

My first question in months :)

None

If $\alpha\ and\ \beta$ be between and $\frac{\pi}{2}$ and if $\cos(\alpha+\beta)=\frac{12}{13}\ and\ \sin(\alpha-\beta)=\frac{3}{5}$ , then find $\sin(2\alpha)$ .

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Mirka

Blazing goIITian

Joined: 13 Aug 2008

Posts: 1313

25 May 2009 10:55:53 IST

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is it 56 / 65 ??

®µD®A

Blazing goIITian

Joined: 12 Apr 2008

Posts: 2717

25 May 2009 10:59:42 IST

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i dont know the answer, but it will be great if you can post the method of solving too. :)

Mirka

Blazing goIITian

Joined: 13 Aug 2008

Posts: 1313

25 May 2009 11:24:01 IST

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Agrima

New kid on the Block

Joined: 22 May 2009

Posts: 17

25 May 2009 20:28:13 IST

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the solution goes like this....acc to d givn details in the ques....we get the result that sine of alpha +beta is=5/13 and cos of alpha-beta is4/5...we have 4 eqs nw...subtracting like eqs we get....2 cos alpha cos beta equal to112/65 and 2sine alpha cos beta=64/65...dividing the two we get...tan alpha=4/7...nw apllyng the formula of sine 2alpha in terms of tan we gt the ans as 56/65....

good ques!!

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