# Re: Law of Sines and Cosines

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Posted by Andrew on October 07, 2002 at 07:15:36:

In Reply to: Re: Law of Sines and Cosines posted by Lisa on October 07, 2002 at 02:14:33:

I just tryed the new formula and it worked like a charm. Thank you.

: are you trying to find Angle A, that formula you used is to find side a which you already know.
: Try cos^(-1) a =(b^2 + c^2 - a^2) /(2bc)
: I tried it for the example below and it worked :) remember to set your calc for degrees.
: a=5, b=6, c=7
: I got this answer ===> 44(degrees) 25'

:
: : The book had an example a=21 b=16.7 c=10.3

: : a^2= b^2 + c^2- 2bc cos(A
: : (21)^2=(16.7)^2 + (10.3)^2 - 2(16.7)(10.3) cos(A
: : 441= 278.89 + 106.09 - 344.02 cos(A
: : cos(A= 441 - 278.89-106.09/-344.02
: : Cos A = -0.1628
: : A=99 (degrees0 22'

: : So I substituted a b and c for a=5, b=6, c=7
: : So then I got a small number like .776 or something. The answer is 44(degrees) 25'

: : What am I doing wrong?

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