input: Write a python function to calculate the area of a right-angled triangle.
  assert area_of_right_triangle(3, 4) == 6.0
  assert area_of_right_triangle(5, 12) == 30.0
  assert area_of_right_triangle(7, 9) == 31.5
output: def area_of_right_triangle(base, height):
      return 0.5 * base * height