3.2.21 cos

cos 

EXPR

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;
$piover180 = $pi/180;

# Print table.

for ($_ = 0; $_ <= 90; $_++) {
    printf "%3d %7.5f\n", $_, cos($_ * $piover180);
}

For the inverse cosine operation, you may use the POSIX::acos() function, or use this relation:

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