Please confirm my answer?
Solve for the unknown part of the triangle, a = 12, b = 15, c = 18 , if parts exist.

C = 92 degrees 20'

Question

Please confirm my answer? 
Solve for the unknown part of the triangle, a = 12, b = 15, c = 18 , if parts exist.

C = 92 degrees 20'

anonymous · Answer

You want to know the angles?

anonymous · Answer

Well I need to know if I got the right answer (92 degrees 20") for C

anonymous · Answer

How did you get it?

anonymous · Answer

I used the law of cosines and I get that cosine of C = 0.25 http://en.wikipedia.org/wiki/Law_of_cosines And 92 doesn't seem plausible

lgbasallote · Answer

dont you have a figure to show?

lgbasallote · Answer

if i remember my trig right there isnt a formula for solving an angle given 3 sides is there?

anonymous · Answer

>>> a = 12
>>> b = 15
>>> c = 18
>>> (c**2 - b**2 - a**2)/(-2.0*a*b)
0.125

sorry 0.125 is the cosine of the angle
@lgbasallote see above

anonymous · Answer

Well I got close to 90. Here are my other options
61°30' 
65°20' 
92°20' 
82°50' 
And no I do not @Igba

lgbasallote · Answer

a 0.125 angle is very hard to believe though.....

anonymous · Answer

working on it, I think you're probably right after all   hang on

anonymous · Answer

Thanks :)

lgbasallote · Answer

wiki says you should do
$$\theta = \cos^{-1} \left(\frac{a^2 + b^2 - c^2}{2ab}\right)$$

lgbasallote · Answer

i think telliot forgot to arc cos or something

lgbasallote · Answer

and i think if you got an answer that's in the choices then it's most probably right

anonymous · Answer

cosine of 83 is about 0.122
@lgbasallote yes that is the law of cosines

anonymous · Answer

I'd go with 82°50'

lgbasallote · Answer

i got 82.82 from wolfram...

anonymous · Answer

Hmm, can you please give me the link to wolfram?

lgbasallote · Answer

anonymous · Answer

Thanks!