input: Write a python function to multiply two 2x2 matrices.
  assert multiply_matrices([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[19, 22], [43, 50]]
  assert multiply_matrices([[0, 1], [1, 0]], [[1, 0], [0, 1]]) == [[0, 1], [1, 0]]
  assert multiply_matrices([[2, 3], [4, 5]], [[1, 0], [0, 1]]) == [[2, 3], [4, 5]]
output: def multiply_matrices(a, b):
      return [[a[0][0] * b[0][0] + a[0][1] * b[1][0], a[0][0] * b[0][1] + a[0][1] * b[1][1]],
              [a[1][0] * b[0][0] + a[1][1] * b[1][0], a[1][0] * b[0][1] + a[1][1] * b[1][1]]]