input: Write a python function to calculate the area of a triangle using Heron's formula.
  assert Triangle(3, 4, 5).area() == 6.0
  assert Triangle(6, 8, 10).area() == 24.0
  assert Triangle(7, 24, 25).area() == 84.0
output: import math
  
  class Triangle:
      def __init__(self, a, b, c):
          self.a = a
          self.b = b
          self.c = c
      
      def area(self):
          s = (self.a + self.b + self.c) / 2
          return math.sqrt(s * (s - self.a) * (s - self.b) * (s - self.c))