New guy and programming problem

[sasa]

(09-01-2018 12:23 PM)Thomas Klemm Wrote:  We can use this difference-to-product formula to calculate...
...
3.807717748e-11

Even result is good enough, there is still too much trouble to get accurate result to the last significant digit with arguments near 90 degree.

The first problem is what is each calculator's internal mantissa length, the second exact representation for PI in internal format (internal conversion from degree to radian) and proper round off mechanism. And as well the used format (decimal or binary floating point) and proper algorithms to calculate trig functions.

The Wolfram Alpha returns:
3.8077177473096929677620869980236729697355177044497495... × 10^-11