A triangle has sides A, B, and C. Sides A and B are of lengths #9# and #7#, respectively, and the angle between A and B is #(7pi)/8 #. What is the length of side C?

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Answer 1 · 2016-11-06T15:48:53

#"C"=15.7#

To answer this question, we have to use the law of cosines.

#"C"^2="A"^2+"B"^2-2"AB"cos("c")=81+49-126cos(7/8pi) =246.4#

#"C"=sqrt264.4=15.7#

Answer 2 · 2016-11-06T15:54:13

2.0359.....

Cosine rule (rearranged for c) = # c^2 = a^2+b^2-2ab*cosC#

#=c= sqrt(9^2+7^2-2*9*7*cos( (7pi)/8))#

=2.035924013