How does sin, log, sqrt work? Trigonometric functions and log might have a table, but what about sqrt?

There's a method for finding the square root of a number. Some code for it was posted on planet source code about a month ago i suppose. Try searching for it there. I'm still not entirely sure how sin and log work. 5^x=25 is the same as log (base 5) 25=x, and somehow i suppose it could deduce x or something. I know there's a method for it out there somewhere, i mean, if it's in a programming language, there's got to be some logical way to do it.

Check out GNU LibC sources, I suppose it's there. Microsoft even give away the source of their runtime library. It's on every good Visual Studio CD :)

As all trigonometric functions can be deduced from sine, here is the sine series

sin x = x - ((x^3)/(3!)) + ((x^5)/(5!)) - ((x^7)/(7!)) + ((x^9)/(9!)) - etc...

cos x = sqrt(1 - ((sin x)^2)) (I think theres a simpler way of getting cos from sin, I just can't remember it

tan x = (sin x)/(cos x)

as for square roots:

log x^1/2 = 1/2 log x

so a numbers square root is 10^(0.5logx)

rdd, those would be very inefficient ways to calculate these functions, so you can be pretty sure nobody uses them in language standard libraries, etc..

http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libm/src/ will show you how openBSD does it.

rdd did u fail high school maths. easiest way to get cos from sin is to use the expression
sin^2x+cos^2x=1

That is what he used, whizkide. Did you fail junior high school algebra? ;)

f**k sorry rdd. gotta go get them lenses.

I remember in a really old programming book that standard libary functions were so slow to calculate sin etc. that at the start of a program requiring their use you should create an array and calculate all the values at initialisation.

Oh, and I should of indicated that my post shows one way of calculating these fuctions, not neccessarily how they are calculated by a computer.

To balance my counter-criticism of whizkide, I must point out that rdd has just typed "should of" and is now an honorary member of the Unwashed Masses Club.

Unwashed Masses Club?

To find the square root of a number can't you just raise it to the 1/2 power? Why do you need to use logarithms? (I must be missing something fundamental here.)

And how exactly do you raise something to a non-integral power? :)

By letting a lower level function than the ones we're talking about figure it out :P ... Ok I getcha.

Pleasepleaseplease... stop adding to this thread!! ;-D

Why not lock it then?

Why not force people to use the wiki by now? :D

We're all waiting for you to put your superior FrontPage into use, of course. :-)

Hahah

Like if you need me for anything :P