SOLUTION: find angle A of the oblique triangle with sides a=13, b=14, and c=15: find angle A of the oblique triangle with sides a=13, b=14, and c=15 Answer by mducky2(13) (Show Source):

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Question 151214: find angle A of the oblique triangle with sides a=13, b=14, and c=15: find angle A of the oblique triangle with sides a=13, b=14, and c=15
Answer by mducky2(13) (Show Source):
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If you need to find an angle when three sides of an oblique triangle are known, use the law of cosines. The equation is:
a2 = b2 + c2 - 2bc cos A
Solve for A
2bc cos A = b2 + c2 - a2
cos A = (b2 + c2 - a2)/(2bc)
A = cos-1[(b2 + c2 - a2)/(2bc)]
A = cos-1[(142 + 152 - 132)/(2*14*15)]
A = 53.13�
Ok now here is my choices
A. 53 Degrees 8' 48''
B 53 Degrees 8' 13''
C. 53 Degrees 7' 48''
D. 53 Degrees 7' 13''
How do I know which one it is?
Answer by jim_thompson5910(35256) (Show Source):
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It looks like the answer is correct (I haven't looked over the problem completely). So to convert 53.13� into degrees minutes and seconds, simply take the decimal portion 0.13 and multiply it by 60 to get . So there are about 7 minutes in 0.13 degrees. Now take the decimal portion 0.8 and multiply it by 60 to get . So there are 48 seconds in 0.8 minutes.

So 53.13� is the same as 53 degrees 7 minutes 48 seconds. So the answer is C.

Here is a good calculator to check your work with (it's towards the bottom of the page).