Cos 36 degrees*

(a) Express in closed form. See Sublime Triangle.

What is "closed form?"
          Express as a real number. Not a decimal approximation. Not the sum of some infinite series.

(b) Prove that


One solution.

Alternative solutions?
Interpretations of either (a) or (b)?

See also    

Return to the EMAT 4600/6600 Page.

* This is problem 4409 in School Science and Mathematics, proposed by Herta T. Freitag, Roanoke, VA.