CODEWITHSUNDEEP
pythonmathtrigonometry
user1080694
user1080694

Reputation: 63

Python's trigonmetric function return unexpected values

import math
print "python calculator"
print "calc or eval"
while 0 == 0:
    check = raw_input() #(experimental evaluation or traditional calculator)
    if check == "eval":
        a = raw_input("operator\n") #operator
        if a == "+":
            b = input("arg1\n") #inarg1
            c = input("arg2\n") #inarg2
            z = b + c
            print z
        elif a == "-":
            b = input("arg1\n") #inarg1
            c = input("arg2") #inarg2
            z = b - c
            print z
        elif a == "/":
            b = input("arg1\n") #inarg1
            c = input("arg2\n") #inarg2
            z = b / c
            print z
        elif a == "*":
            b = input("arg1\n") #inarg1
            c = input("arg2]n") #inarg2
            z = b * c
            print z
        elif a == "^":
            b = input("arg1\n") #inarg1
            c = input("arg2\n") #inarg2
            z = b ** c
        elif a == "sin":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.sin(b))
            print var
        elif a == "asin":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.asin(b))
            print var
        elif a == "cos":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.cos(b))
            print var
        elif a == "acos":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.acos(b))
            print var
        elif a == "tan":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.tan(b))
            print var
        elif a == "atan":
            b = input("arg1\n") #inarg1
            var = math.degrees(math.atan(b))
            print var
    elif check == "calc" :
        x = input() #takes input as expression
        print x #prints expression's result

Isn't the sine of 90 degrees 1? With this it shows up as something around 51.2? Google's calculator does this too? BTW: this is my python calculator

            b = input("arg1\n") #inarg1
            var = math.degrees(math.sin(b))
            print var

This one and other trig functions are the problem. For the most part, this was just a simple python calculator, but I wanted to add some trig functions.

Upvotes: 4

Views: 6159

Answers (6)

sarnold
sarnold

Reputation: 104050

Most math functions, including Python's math functions, use radians as the measure for trigonometric routines.

Compare:

>>> math.sin(90)
0.8939966636005579
>>> math.sin(3.1415926535)
8.979318433952318e-11
>>> math.cos(180)
-0.5984600690578581
>>> math.cos(2*3.1415926535)
1.0
>>>

Upvotes: 3

Sven Marnach
Sven Marnach

Reputation: 601609

You don't want o convert the return value of sin() to degrees -- the return value isn't an angle. You instead want to convert the argument to radians, since math.sin() expects radians:

>>> math.sin(math.radians(90))
1.0

Upvotes: 10

David Schwartz
David Schwartz

Reputation: 182761

        var = math.degrees(math.sin(b))

This code does not do what you think it does. It takes the sin of b and then converts that answer (which is not in radians!) from radians to degrees.

The sin of 90 radians is .894. .894 radians is 51 degrees. So that's why you get that answer, but it's all wrong.

You probably want:

        var = math.sin(math.radians(b))

Upvotes: 2

K Mehta
K Mehta

Reputation: 10543

Convert your input from degrees to radians before calling math.sin

Upvotes: 2

detly
detly

Reputation: 30332

You are using degrees, but the sin function expects radians (see the documentation: help(math.sin)). 90° is 𝜋/2.

>>> import math
>>> math.sin(math.pi/2)
1.0
>>> math.radians(90) - math.pi/2
0.0

Upvotes: 2

Winston Ewert
Winston Ewert

Reputation: 45039

Python's sin and cos take radians not degrees. You can convert using the math.radians function. Basically, you are using the wrong units.

Upvotes: 3

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