<PRE><B>Question 681180</B>
A triangle has 3 measurements from A,B,C. Length AB=18, BC=13 and CA=16. What&#39;s the angle in between the measurements 16 and 18.

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Law of Cosines:
a^2 = b^2 + c^2 - 2bc*cos(A)
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cos(A) = [b^2 + c^2 -a^2]/(2bc)
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Notice the b and c are the sides that make angle A
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Your Problem:
cos(A) = [16*2+18^2-13^2]/(2*16*18) = 0.7135
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A = cos^-1(0.7135) = 39.08 degrees
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Cheers,
Stan H.
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