input: Write a function to compute the area of a circle given its radius. The function should return the computed area.
  
  import math
  
  def area_circle(radius):
   return math.pi * (radius ** 2)
  
  assert area_circle(5) == 78.53981633974483
  assert area_circle(0) == 0
  assert area_circle(1) == 3.141592653589793
output: import math
  
  def area_circle(radius):
   return math.pi * (radius ** 2)