math domain error in python when caluclating angles

Question

trying to calculate all kind of triangle's angles by given sides. I have all the agorithms to do so, one slight problem is having a 'math domain error' which i can't find. Appreciate any help :)

from math import *
def angles(a, b, c):
    if a + b <= c or a + c <= b or c + b <= a:
        return [0, 0, 0]
    elif a == b == c:
        return [60,60,60]
    tempLst = []
    d = max(a,b,c) #To know which angle is the largest
    if a == d:
        if (b ** 2 + c ** 2) < d**2: #To know wether a triangle is an obtuse triangle
           tempLst.append(round(degrees(acos((c**2 - a**2 - b**2) / (-2 * c * b)))))
           tempLst.append(round(asin(a/sin(tempLst[0])*b)))
        else:    
           tempLst.append(round(degrees(asin(c/a))))
           tempLst.append(round(degrees(asin(b/a))))
    elif b == d:
        if (a**2+c**2) < d**2:
            tempLst.append(round(degrees(acos((c**2 - a**2 - b**2)/-2*c*a))))
            tempLst.append(round(asin(b/sin(tempLst[0])*a)))
        else: 
            tempLst.append(round(degrees(asin(c/b))))
            tempLst.append(round(degrees(asin(a/b))))
    else:
        if (b**2+a**2) < d**2:
            tempLst.append(round(degrees(acos((c**2 - a**2 - b**2)/-2*a*b))))
            tempLst.append(round(asin(c/sin(tempLst[0])*b)))
        else: 
            tempLst.append(round(degrees(asin(a/c))))
            tempLst.append(round(degrees(asin(b/c))))
    tempLst.append(180 - tempLst[0] - tempLst[1])
    return tempLst

Error: ValueError: math domain error

angles, 25

when trying to input these values: angles(11, 20, 30) ---> "Unhandled exception"

Thank you all

This problem is more related to trigonometry than programming. You have to understand how the trigonometric functions work (in math, not Python). For example, you can't do calculate `acos` for a anything outside of the range `[-1, 1]` — DeepSpace, May 14 '18 at 20:43
`(c**2 - a**2 - b**2)/-2*a*b` gives `-41690.0`. `acos` takes a value between `-1` and `1` — ktzr, May 14 '18 at 20:45
In the future, please try to debug on your own. It took me less than a minute (and I'm sure that for @ktzr as well) to find the offending line and print the value that is being passed to `acos` — DeepSpace, May 14 '18 at 20:48

score 1 · Accepted Answer · answered May 14 '18 at 20:55

Your trig is off. Use the Law of Cosines

from math import *


def angles(a, b, c):
    if a + b <= c or a + c <= b or c + b <= a:
        return [0, 0, 0]
    elif a == b == c:
        return [60, 60, 60]
    tempLst = [
        round(degrees(acos((a ** 2 + b ** 2 - c ** 2) / (2 * a * b)))), # C
        round(degrees(acos((b ** 2 + c ** 2 - a ** 2) / (2 * b * c)))), # A
        round(degrees(acos((c ** 2 + a ** 2 - b ** 2) / (2 * c * a))))  # B
    ]

    return tempLst


print(angles(11, 20, 30))
# -> [149, 11, 20]

math domain error in python when caluclating angles

1 Answers1