Really amatuer to C++, trigonometry trouble

Sancho · #1 12-Jan-2005, 14:10

Heya all,

I'm really not very good at C++ at all, the most that I do is dabble in it, but at the moment I'm just trying to set up a program where I can do some trigonometry a lot easier than having to use a scientific calculator.

The problem that I'm having is with using arctan, arc-cosine and arcsine. normal tan(x*Pi/180) is working fine (as I know you have to convert into radians), but the problem is that no matter how I enter my value to use as atan(x)
it doesn't give a corrent answer. I've tried entering it as radians, both converting it before and by using:
atan(x*Pi/180)

and I've also tried the other way, converting from radians to decimal again, using x*180/pi

I just can't seem to get any answer that is correct out of it.

Sorry if this seems like a really simple thing to most, but I just can't get it to work.

davekw7x · #2 12-Jan-2005, 17:13

Quote:

Originally Posted by Sancho

Heya all,

I
The problem that I'm having is with using arctan, arc-cosine and arcsine. normal tan(x*Pi/180) is working fine (as I know you have to convert into radians), but the problem is that no matter how I enter my value to use as atan(x)

All trig function angles are in radians, just as a real mathematician would do it.

CPP / C++ / C Code:

#include <stdio.h>
#include <math.h>

int main()
{
  double Pi;
  double x;
  double y;

  /* here's a way to get pi without typing in a bunch of digits */
  Pi = 4.0 * atan(1.0);

  printf("Pi             = %.15f\n", Pi);

  x = Pi / 4.0;
  printf("Pi / 4.0       = %f\n", x);
  y = sin(x);
  printf(" sin(%f) = %f\n", x, y);
  x = asin(y);
  printf("asin(%f) = %f radians (%f degrees)\n\n", y, x, x * 180.0 / Pi);

  x = Pi / 8.0;
  printf("Pi / 8.0       = %f\n", x);
  y = tan(x);
  printf(" tan(%f) = %f\n", x, y);
  x = atan(y);
  printf("atan(%f) = %f radians (%f degrees)\n\n", y, x, x * 180.0 / Pi);

  return 0;
}

Regards,

Dave

Sancho · #3 13-Jan-2005, 03:16

Thanks dave, thats cleared it up a hell of a lot for me

Going to break out my old maths work books from A-level and try to remember how to do radians

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