input: Write a python function to evaluate a mathematical expression for a given value of x.
  assert evaluate_expression('x**3 + 2*x**2 + 3', 2)==19
  assert evaluate_expression('x**3 - x', 3)==24
  assert evaluate_expression('2*x + 5', 5)==15
output: def evaluate_expression(expression, x):
      return eval(expression)