Write a function to find the perimeter of a pentagon.
import math
def perimeter_pentagon(a):
  perimeter=(5*a)
  return perimeter
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find the perimeter of a pentagon.
import math
def perimeter_pentagon(a):
  perimeter=(5*a)
  return perimeter[/INST]assert perimeter_pentagon(5)==25
assert perimeter_pentagon(10)==50
assert perimeter_pentagon(15)==75</s>