input: Write a function to calculate the area of a circle given the radius as input. The function should use the formula \( \text{area} = \pi \times \text{radius}^2 \).
  
  import math
  
  def area_circle(radius):
   return math.pi * (radius ** 2)
  
  assert area_circle(5) == 78.53981633974483
  assert area_circle(0) == 0.0
  assert area_circle(1) == 3.141592653589793
  assert area_circle(3.5) == 38.48451000647496
  assert area_circle(-2) == 12.566370614359172
  
output: import math
  
  def area_circle(radius):
   return math.pi * (radius ** 2)