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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): Solution Comment 12 of 12 |
(In reply to re: Solution by Brian Smith)

More easily than from law of cosines, 'c = a*cosB + b*cosA' follows from dividing the triangle into two right triangles (one of which may be "negative" in the case of A or B being obtuse).

I had trouble initially seeing where this came from.

  Posted by Charlie on 2007-11-21 09:10:11
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