CODEWITHSUNDEEP
androidcmathandroid-ndkcmath
Hari Krishna Ganji
Hari Krishna Ganji

Reputation: 1677

In C, tan(30) gives me a negative value! Why?

I observe that my tan(float) function from the cmath library is returning a negative value.

The following piece of code, when run :

    #include <cmath>
    ....

    // some calculation here gives me a value between 0.0 to 1.0.
    float tempSpeed = 0.5; 

    float tanValue = tan(tempSpeed * 60);

    __android_log_print(ANDROID_LOG_INFO, "Log Me", "speed: %f", tanValue);

Gives me this result in my Log file:

    Log Me: speed `-6.4053311966`

As far as I remember 

    tan(0.5*60) = tan(30) = 1/squareroot(3);

Can someone help me here as in why I am seeing a negative value? Is it related to some floating point size error? Or am I doing something really dumb?

Upvotes: 13

Views: 8938

Answers (3)

rav3451
rav3451

Reputation: 41

I guess in C the tan Function requires you to Input Radians as an argument and not The actual degree value.

so for Tan 30 , you would have to convert your 30 degrees to radian. Keep in Mind that 360 degrees is 2*Pi radian so 30 degress would be (1\6 * Pi)th of a radian.

so tan(1\6 * Pi) would give you the correct answer. where Pi is 3.142

Upvotes: 1

Jonathan Grynspan
Jonathan Grynspan

Reputation: 43472

That's the tangent of your angle (30 radians.) if you are looking for the tangent of 30 degrees, you must convert your angle to radians first.

Upvotes: 7

K-ballo
K-ballo

Reputation: 81379

In C, tan and other trigonometric functions expect radians as their arguments, not degrees. You can convert degrees to radians:

tan( 30. * M_PI / 180. ) == 0.57735026918962576450914878050196

Upvotes: 46

Related Questions