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Math problem in C

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Join Date: Sep 2004

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ray96

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Newbie Poster

Math problem in C

Oct 8th, 2004

Hi! I had 1 problem in C, now I have another one. :o
Please bear with me. I am learning the C language.

Please run the following calculation in a scientific calculator. When the "=" sign is shown at the end of the calculation, be sure to press the = button on the calculator. Asin is labeled Sin -1 on some calculators. It dosn't matter if you don't have a scientific calculator.

((292.797 sin)*0.39777)asin=

The answer should be: -21.6685752754108925

Here is the same calculation in C. This is the way I do it:

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

main()
{
double math;

math=sin(292.797) * asin(0.39777);

printf("The result is %f",math);

return 0;

}

Ok, why aren't the 2 calculations the same? I need them the same. I have tried using different types of variables, I have tried converting radians to degrees, (math * 180 / PI) I have tried other things too, but to no avail. I have even tried doing a simple calculation like the following, to see if I did a mistype:

math=sin(1);

Even the above problem won't compute the same. It'll work fine for the basic calculations (+, -. x, -).

I think my problem might be converting radians to degrees (not sure). I have heard several calculations on converting radian numbers to degrees, and I have tried all of them. None have seemed to work.

I would appreciate ANY help on how I can get the 2 calculations to be the same.

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Join Date: Aug 2004

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cosi

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Re: Math problem in C

Oct 8th, 2004

Hi Ray,

it looks like your caculator is in RPN (a.k.a. Reverse Polish Notation) mode.

In order to relect the same sequence of operations in C, you should convert to standard notation:

asin (0.39777 * sin (292.797)) If you then wanted to convert the answer into Degrees instead of radians, simply multiply the answer by 180 / PI.

PI = 3.14.....
180 / PI * asin (0.39777 * sin (292.797))

I hope I understood your question. and I hope this helps.

Ed

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Originally Posted by ray96

((292.797 sin)*0.39777)asin=

The answer should be: -21.6685752754108925

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Join Date: Sep 2004

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ray96

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Re: Math problem in C

Oct 9th, 2004

Thank You for your response! I will try what you said

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vegaseat

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Re: Math problem in C

Oct 10th, 2004

You have to be careful with radians and degrees, don't get them mixed up!

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
// result is supposed to be -21.6685752754108925 ?
// my casio calculator and the computer says -21.51209184
 
#include <stdio.h>
#include <math.h>
 
int main(void)
{
  double math, PI, x; 
 
  PI = atan(1) * 4.0;    // a little old fashioned trickery to get PI
  x = 292.797 * PI/180;  // degrees to radians
 
  math = asin(sin(x) * 0.39777);
 
  printf("The result is %f radians",math); 
 
  math = math * 180 / PI;   // radians back to degrees 
 
  printf("\nThe result is %f degrees",math);
 
  getchar();
  return 0;
}
// result is supposed to be -21.6685752754108925 ?
// my casio calculator and the computer says -21.51209184

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

int main(void)
{
  double math, PI, x; 
  
  PI = atan(1) * 4.0;    // a little old fashioned trickery to get PI
  x = 292.797 * PI/180;  // degrees to radians
  
  math = asin(sin(x) * 0.39777);

  printf("The result is %f radians",math); 
  
  math = math * 180 / PI;   // radians back to degrees 

  printf("\nThe result is %f degrees",math);
  
  getchar();
  return 0;
}

You may have slipped on one of them darn numbers on those tiny calculator keys, hombre! Close enough! Remember, computers never make missteaks!