Math.cos() gives wrong result

Question

According to Wolfram Mathematica: cos(50) = 0.6427876096865394;

But this code in Java:

    System.out.println(Math.cos(50));

gives 0.9649660284921133.

What is wrong with java.lang.Math?

Solution 1

Math.cos() expects the parameter to be in radians. This will return the result you need:

Math.cos(Math.toRadians(50));

Solution 2

Math.cos() uses radians, so to get your expected result you need to do

System.out.println(Math.cos(Math.toRadians(50)));

Solution 3

Most Java trigonometric functions expects parameters to be in radians. You can use Math.toRadians() to convert:

System.out.println(Math.cos(Math.toRadians(50)));

Solution 4

Degrees <> radians...........

View more solutions

Comments

[Ignacio Contreras Pinilla]

+1. Just for reference, as OP was talking about wolfram wolframalpha.com/input/?i=cos%2850rad%29

[phant0m]

Wolfram Alpha does not use degrees by default! Rather, it is trying to be clever.

[Manu]

What is Wolfram Alpha default, degree or radian or ... ? Is there another base ? Can you give more argument about what you write ? Your comment does not give any information in fact ! My response does not respond to the initial question, so ok for "-1" flag but It give more information usefull about this conversation, I think.

[Manu]

What this answer means ? Degree is equivalent to radian... but 1 degree = 0.0174532925 radians

[phant0m]

Wolfram Alpha tries to guess whether your input is in radians or degrees: If the value is below 5, it seems to interpret it as radians, if it's larger or equal than 5, it interprets it as degrees ;) I have taken the liberty to correct the output that Java actually produces upon executing that code.

[phant0m]

My -1 was mainly due to this: I don't know exactly what the meaning of these results but for me..., apart from it not being a proper answer to the question. Given your code, you seem to try to guess what is happening, instead of having an understanding for it. This is further demonstrated by this: Math.cos(Math.toDegrees(50)) You feed a function that expects radians the value, that you get after converting 50 radians to degrees, a value that is completely random.

[phant0m]

@Manu The but part in your comment is why they are not equivalent ;) It's like saying kilos and stone are equivalent. They measure the same quantity, sure, but in different ways.

[Manu]

I'm agree with you... It is a mistake from me to feed by degree a method that expect radian. Like I said, I agree with people who give -1 AND give information about this : I expect it cannot be so easy to give -1. So thanks for explain, @phant0m. I will correct my answer so.

[Manu]

Do I have to aks an other question and make a relation between mine and this question if I try/want to understand why these method return different results ?

[bestsss]

new Double(50) servers no purpose at all.

[Stevoisiak]

Is there a version of Math.cos() in Java that works with Degrees, or do we constantly need to remember to manually convert degrees to radians?