math.cos(x)没有返回正确的值? [英] math.cos(x) not returning correct value?

问题描述

我刚刚开始使用python，但是在使用一个非常基本的程序时遇到了困难.我想计算-20度的余弦.据我了解，默认值以弧度表示，因此这是我尝试的以下代码:

I just started using python, and am having difficulty with a very basic program. I want to calculate the cosine of -20 degrees. It is my understanding that the default value is in radians, so this is the following code i tried:

import math 


print math.cos(math.degrees(-20))

这将输出(-.7208 ...)，答案实际上是(.9397 ...).我确定这是一个非常基本的解决方案，但是我尝试了很多不同的方法，但不会输出正确的结果.预先感谢！

This outputs (-.7208...), where the answer is actually (.9397...). I'm sure this has a pretty basic solution but I've tried so many different things and it will not output the correct results. Thanks in advance!

推荐答案

根据

数学.度(x)

math.degrees(x)

将角度 x 从弧度转换为度.

Convert angle x from radians to degrees.

这意味着您试图将-20弧度转换为不需要的度数.

That means you are attempting to convert -20 radians to degrees which isn't desired.

也根据文档:

math.cos(x)

math.cos(x)

返回 x 弧度的余弦.

这意味着 math.cos 以弧度而不是度来查找传递的参数的余弦.这意味着您的代码当前将度数更改为-20弧度，然后将其余弦视为弧度...您可以看到为什么会出现问题.

This means math.cos finds the cosine of the passed argument in radians, not degrees. That means your code currently changes -20 radians to degrees, then finds the cosine of that as if it were radians... you can see why that's a problem.

您需要将-20度转换为弧度，然后找到余弦.使用 math.radians :

You need to convert -20 degrees to radians, and then find the cosine. Use math.radians:

math.cos(math.radians(-20))

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