Bit of basic maths. You are using a power series to approximate sine This works by taking an expansion about a fixed point, usually zero. It only works well around that point. If you get far away it works badly. You need to exploit the cyclic nature of the trignometrical functions i.e. Sin x = sin ((2 * pi) + x) = sin ((4 * pi) + x) Essentially consider the shift in multiples of 2 * pi and calculate the value of x nearest to zero. See http://en.wikipedia.org/wiki/Taylor_series The diagram on the top right is very instructive. Paul -----Original Message----- From: beginners-bounces@haskell.org [mailto:beginners-bounces@haskell.org] On Behalf Of Jeffrey Drake Sent: Thursday, October 16, 2008 9:47 AM To: Haskell Beginners Subject: [Haskell-beginners] Mathematical Blundering I have defined myself a set of functions to test: fact 1 = 1 fact n = n * (fact $ n - 1) sine x = x - (x^3/(fact 3)) + (x^5/(fact 5)) - (x^7/(fact 7)) Where my code is 'sine' and the prelude's is sin: *Main> sine 1 0.841468253968254 *Main> sin 1 0.8414709848078965 *Main> sine 2 0.9079365079365079 *Main> sin 2 0.9092974268256817 *Main> sine 3 9.107142857142847e-2 *Main> sin 3 0.1411200080598672 *Main> sine 4 -1.3841269841269837 *Main> sin 4 -0.7568024953079282 After 2 they seem to diverge rather rapidly, and I am not sure why. Any ideas? I would have thought that 4 terms would have been enough. - Jeff. _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners