How can the sum of three cosines equal 1?

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The discussion centers on proving how the sum of three cosines can equal 1, referencing a specific document for context. The original poster seeks assistance in understanding this mathematical concept. A participant suggests using the Pythagorean theorem to express the length of a point in relation to its coordinates defined by the cosines. This approach leads to the desired relation, confirming the original poster's understanding. The interaction concludes with the original poster expressing gratitude for the help received.
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If OP=d, the coordinates of P are (cos α1,cos α2,cos α3)d. Now, express the length of OP using Pythagoras and you get the desired relation.
 
Norwegian said:
If OP=d, the coordinates of P are (cos α1,cos α2,cos α3)d. Now, express the length of OP using Pythagoras and you get the desired relation.

Got it! Thanks!
 

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