How do you find the exact value of cos (pi)?

How do you find the exact value of cos (pi)?

          %pi=3. 14159265. . . % is a transcendental number.  This is a limit problem of %x to pi% of cos x.  cos x is continuous at %x = pi%.  Both  %cos pi_+ and cos pi_( - )% approach to the same limit %-1%.                                     <h4 class=answerHeader>Explanation:</h4>                                      The Calculator value of <mathjax>%cos pi = cos 180^o = -1%</mathjax> is by truncation and rounding of (say) 10-sd <mathjax>%-1. 000000000  %</mathjax> approximation obtained from an approximating truncated continued fraction of quadratics.  The error (if any) in the knocked out part of the processed string and i<br></br>is hiding. .  <mathjax>%180^o%</mathjax> is converted to x = 3. 14159263. . . (truncated) and used in the approximation process. . Glory to Numerical Analysis Experts of older generation who perfected all these approximations of functions, for use in electronic hand devices. .