input: Write a function to calculate the area of a triangle given the lengths of its sides.
  assert areaTriangle(3, 4, 5) == 6.0
  assert areaTriangle(7, 24, 25) == 84.0
  assert areaTriangle(5, 12, 13) == 30.0
output: import math
  
  def areaTriangle(a, b, c):
      s = (a + b + c) / 2
      return math.sqrt(s * (s - a) * (s - b) * (s - c))