SOLUTION: In triangle ABC, a=8, b=9, and cosC= 2/3. Find c.

Algebra ->  Trigonometry-basics -> SOLUTION: In triangle ABC, a=8, b=9, and cosC= 2/3. Find c.      Log On


   

Question 1105984: In triangle ABC, a=8, b=9, and cosC= 2/3. Find c.
Answer by ikleyn(52835) About Me  (Show Source):
You can put this solution on YOUR website!
.
Cosine law: 

c^2 = a^2 + b^2 - 2ab*cos(C) = 8^2 + 9^2 - 2%2A8%2A9%2A%282%2F3%29.


Complete these calculations on your own.

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On cosine law,  see the lessons
    - Proof of the Law of Cosines revisited
    - Solve triangles using Law of Cosines
in this site.