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Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: chocoholic4lyf on October 31, 2009, 12:03:38 PM

Title: trig problem!!!
Post by: chocoholic4lyf on October 31, 2009, 12:03:38 PM

Let x and y be real numbers such that:
sin(x) + sin(y)= a
cos(x)+cos(y)= b

determine sin(x+y) and cos(x+y).
any help would be appreciated :D
thanks in advance

Title: Re: trig problem!!!
Post by: cth on October 31, 2009, 12:48:09 PM

You need to use the equations (see http://en.wikipedia.org/wiki/Cosinus):
cos²x + sin²x = 1
cos(x+y) = cos(x)cos(y) - sin(x)sin(y)
sin(x+y) = sin(x)cos(y) + cos(x)sin(y)

With the equations you already have:

Quote from: chocoholic4lyf on October 31, 2009, 12:03:38 PM

sin(x) + sin(y)= a
cos(x)+cos(y)= b

and a bit of work up, you should be able to solve your problem.

btw, I didn't notice there was a math forum as well. Nice  :D

Title: Re: trig problem!!!
Post by: Ranadeep on November 01, 2009, 05:11:33 AM

Some more formula  you might need : )

2Sinx Cosx = Sin(2x)
Cos²X-Sin²X = Cos(2x)
Also take a note on Trigonometric transformations : )