input: Write a python function to compute the gradient of the function 1/x using the backward method of NNClass.
  assert NNClass().backward(2) == 2 * (1 / NNClass().x)
  assert NNClass().backward(0) == 0 * (1 / NNClass().x)
  assert NNClass().backward(-3) == -3 * (1 / NNClass().x)
output: def gradient_backward(x):
      return x * (1 / x)