input: Write a python function to differentiate a polynomial equation represented as a string.
  assert differentiate("3x2+2x1+1x0") == "+6x1+2"
  assert differentiate("5x3+4x2+3x1+2") == "+15x2+8x1+3"
  assert differentiate("7x4+6x3+5x2+4x1+3") == "+28x3+18x2+10x1+4"
output: def differentiate(equation: str) -> str:
      terms = equation.split('+')
      result_terms = []
      for term in terms:
          coefficient, power = map(int, term.split('x'))
          if power != 0:
              new_coefficient = coefficient * power
              new_power = power - 1
              result_terms.append(f"+{new_coefficient}x{new_power}")
          elif power == 0 and coefficient != 0:
              result_terms.append(f"+{coefficient}")
      return ''.join(result_terms)