sin cos tan
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Thread: sin cos tan

  1. #1
    Join Date
    Aug 1999
    Location
    Gastonia, NC
    Posts
    391

    sin cos tan

    I'm trying to do some pie chart math,
    and doing so I'm using the sin() and cos()
    functions.

    My delima is, if I use sin() on an angle of 18
    for example, the sin() function returns

    -0.75098724677168

    if you put 18 in Calculator and press the SIN
    button, it gives you

    0.30901699437494742410229341718282

    The one from Calculator is the one I'm after
    to get my math right, what's up?

    Also, if you go to the def of sin in MSDN
    it shows this little snipplet:


    Example
    /* SINCOS.C: This program displays the sine, hyperbolic
    * sine, cosine, and hyperbolic cosine of pi / 2.
    */

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

    void main( void )
    {
    double pi = 3.1415926535;
    double x, y;

    x = pi / 2;
    y = sin( x );
    printf( "sin( %f ) = %f\n", x, y );
    y = sinh( x );
    printf( "sinh( %f ) = %f\n",x, y );
    y = cos( x );
    printf( "cos( %f ) = %f\n", x, y );
    y = cosh( x );
    printf( "cosh( %f ) = %f\n",x, y );
    }




    Output

    sin( 1.570796 ) = 1.000000
    sinh( 1.570796 ) = 2.301299
    cos( 1.570796 ) = 0.000000
    cosh( 1.570796 ) = 2.509178


    If I punch in the numbers in Calculator, none of
    this works out right. Even based on solely the
    bottom output, Calc says the sin(1.570796) is
    0.027412127890540702705615104925336 and not
    1.000000000.

    Thanks...


    *DM*
    AIM/AOL: EdisonCPP
    ICQ: 39184886 - ID EdisonCPP
    Email: edisoncpp@carolina.rr.com
    sedison@protronix.com

  2. #2
    Join Date
    Aug 2000
    Location
    West Virginia
    Posts
    7,564

    Re: sin cos tan

    your calculator is using the angle as DEGREES not RADIANS.
    It should have an option to change this.



  3. #3
    Join Date
    Jul 2001
    Location
    Otaki, New Zealand
    Posts
    303

    Re: sin cos tan

    The difference is that what you get when you do sin(18) is in fact sin (18 Radians) which is different from sin(18 degrees).

    If you put your calculator into Rad mode and then repeat sin(18) you get the answer -0.75098.

    A lot of maths calculations are based on Radians and are expressed in terms of pi.

    2*pi = 360 degrees
    =>
    1 Radian = 57.2958 degrees
    pi = 180 degrees
    pi/2 = 90 degrees
    sin(90) = sin(pi/2) = 1.0

    The MSDN help for sin does sya that the parameter x is the 'Angle in Radians'

    Regards
    Alan



  4. #4
    igbrus is offline Elite Member Power Poster
    Join Date
    Aug 2000
    Location
    Los Angeles
    Posts
    4,658

    Re: sin cos tan

    sin is work with radians and your calcularor - with degrees! Set calculator to radians and see the same results

    Rating isn't important...But gurus respect it and keep high

  5. #5
    Join Date
    Aug 1999
    Location
    Gastonia, NC
    Posts
    391

    Re: sin cos tan

    So how do I use Degrees with sin()?
    You were right about calc.exe, it
    then gave the same result.

    *DM*
    AIM/AOL: EdisonCPP
    ICQ: 39184886 - ID EdisonCPP
    Email: edisoncpp@carolina.rr.com
    sedison@protronix.com

  6. #6
    Join Date
    Jul 2001
    Location
    Otaki, New Zealand
    Posts
    303

    Re: sin cos tan

    1 degree = pi/180 radians;
    Store it as a constant and multiply before calling sin,cos etc.


  7. #7
    Join Date
    Aug 2000
    Location
    West Virginia
    Posts
    7,564

    Re: sin cos tan


    float angle_in_degrees = 18.0f;
    //
    // convert degrees to radians ... 3.14159 (PI) radians = 180 degrees
    //
    float angle_in_radians = angle_in_degrees * 3.14159f/ 180f;
    //
    //
    // use : sin(angle_in_radians);
    //







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