Tomasz Ksepka Tomasz Ksepka - 6 months ago 10
Python Question

Law of cosines returns 90 degrees for all angles in a triangle?

I'm working on an assignment where I make a class called Triangle that takes in three sides and returns information about the triangle. Specifically, I am trying to calculate the three angles within the triangle, but for some reason I am getting 90 degrees for all angles, which is impossible. I have gone over my code tons of times but can't find the mistake and would greatly appreciate some help. Thank you.

from math import acos, degrees, sqrt
import turtle

class Triangle:

def __init__(self, side_a=None, side_b=None, side_c=None):

self.side_a = side_a
self.side_b = side_b
self.side_c = side_c

def is_triangle(self):
return ((self.side_a + self.side_b) > self.side_c) \
and ((self.side_a + self.side_c) > self.side_b) \
and ((self.side_b +self.side_c) > self.side_a)

def perimeter(self):
if self.is_triangle():
return self.side_a + self.side_b + self.side_c
else:
return None

def area(self):
if self.is_triangle():
s = self.perimeter()/2
print s
return sqrt((s*(s-self.side_a)*(s-self.side_b)*(s-self.side_c)))
else:
return None

def a_angle(self):
if self.is_triangle():
return degrees(acos((self.side_b**2 + self.side_c**2 - self.side_a**2)/(2*self.side_b*self.side_c)))
else:
return None

def b_angle(self):
if self.is_triangle():
return degrees(acos((self.side_c**2 + self.side_a**2 - self.side_b**2)/(2*self.side_c*self.side_a)))
else:
return None

def c_angle(self):
if self.is_triangle():
return degrees(acos((self.side_a**2 + self.side_b**2 - self.side_c**2)/(2*self.side_a*self.side_b)))
else:
return None

def angle(self):
return self.a_angle(), self.b_angle(), self.c_angle()

def __str__(self):
pass






tri = Triangle(11, 7, 9)
print tri.is_triangle()
print tri.perimeter()
print tri.area()
print tri.a_angle()
print tri.b_angle()
print tri.c_angle()
print tri.angle()

Answer

In Python 2, division of integers by default truncates the result to an integer, so something like 5/2 will equal 2. In your case, dividing the sides results in zero.

The simplest way to fix it is to do from __future__ import division at the very beginning of your file. This makes division always return a float.

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