如何定义python函数

Question

So I am new to Python and have to take a class in it for college credits. We were given an assignment to do at home (we are allowed to go online for help etc) and part of this involved defining a function. I'm not very good at coding/computers in general and I'm having a lot of difficulty in trying to do so.

How would I go about defining a function so cos(a,b,c) = cos(a - c) - ab? I've tried everything, and I wouldn't be outright asking people for help if I wasn't desperate.

I know that function may seem easy to some but I'm just not good at this at all. This is what I tried (don't laugh!)

def np.cos(a, b, c):   
"""
Given three variables, rearrange them to create new equation
>>>np.cos(d,e,f)
np.sin(d - f) - e*d
>>>np.cos(1,2,3)
np.cos(1 - 3) - 2*3
"""
if np.cos(a, b, c):
    return np.cos(a - c) - b*a 

As you can clearly see, I'm not sure what I'm doing. Any advice/tips would be greatly appreciated. Thank you :)

Answer 1

You can use math.cos() to determine the cosine value of anything in your function.

import math 
def cos(a,b,c):
    return math.cos(a-c) - a*b

print cos(1,2,3) 

Two things to look here:

1. Although I have named my function cos to show you the difference between cos and math.cos , you should name your function to something else like cosOfthree to avoid naming conflicts.
2. Always look at your indentation in python code. Instructions inside function definition should be indented.

Answer 2

You can import math and do something like this

import math
def trig(a,b,c):
    return math.cos(a-c)-a*b
a,b,c= map(eval,raw_input().split())
trig(a,b,c)