Given a triangle with b=4, c=10, and a=84*, what is the length of a? round to the nearest tenth. i know you have to use the law of cosines, but i am really confused on how to do this.

We are given with two sides b=4, c=10 and an angle of 84 degrees. Using cosine law to determine the third side, we use the formula: 
a^2 = b^2 + c^2 -2bc cos thetaa^2 = 4^2 + 10^2 -2*4*10 cos 84a^2 = 107.64a   = 10. 37 units 

I'm a bit puzzled here because they did not provide you with any measures of the other angles, so i am unable to provide a theorem or postulate to support my answer, but i'd say 90 degrees because it looks closer to a right angle than anything.