input: Write a function that computes the area of a circle given its radius. The function should use the formula for the area of a circle, which is π * radius^2. If the radius is negative, the function should return an error message.
  assert area_circle(5) == 78.54
  assert area_circle(10) == 314.16
  assert area_circle(-5) == 'Error: Radius cannot be negative'
  assert area_circle(0) == 0
output: def area_circle(radius):
      if radius < 0:
          return 'Error: Radius cannot be negative'
      return round(3.1416 * radius ** 2, 2)