Programming Perl, 4th Edition

cos

cos EXPR
cos

This function returns the cosine of EXPR (expressed in radians). For example, the following script will print a cosine table of angles measured in degrees:

# Here's the lazy way of getting degrees–to–radians

$pi = atan2(1,1) * 4;
$pi_over_180 = $pi/180;

# Print table
for ($deg = 0; $deg <= 90; $deg++) {
    printf "%3d %7.5f\n", $deg, cos($deg * $pi_over_180);
}

For the inverse cosine operation, use the acos function from the Math::Trig or POSIX modules, or else use this relation:

sub acos { atan2( sqrt(1 – $_[0] * $_[0]), $_[0] ) }