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Any triangle, Trigonometric function - second episode! (Posted on 2007-11-18) Difficulty: 3 of 5
Prove that in any triangle cos(A)+cos(B)+cos(C)>1

See The Solution Submitted by Chesca Ciprian    
Rating: 3.0000 (1 votes)

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re(2): non-Euclidean case? | Comment 5 of 12 |
(In reply to re: non-Euclidean case? by brianjn)

You are treading in the area of Riemann's spherical geometry. Riemann's spherical geometry is said to complete the triad of the different geometries -- no parallels and the angle sum is (always) more than 180 degrees.  I was making reference to Gauss' non-Euclidean geometry where parallel lines intersect at one point only and the angle sum of a triangle is (always) less than 180 degrees. 

But, then perhaps I meant to be making reference to Riemann's spherical geometry? My lack of knowledge of the two geometries (and even in Euclidean geometry) leaves me the one who might be treading dangerously.

Edited on November 19, 2007, 7:43 am
  Posted by Dej Mar on 2007-11-19 07:33:47

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