mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="12px"><mrow><msup><mfenced open="[" close="]" separators="|"><msup><msqrt><mn>81</mn></msqrt><mn>2</mn></msup></mfenced><mn>2</mn></msup><mo>=</mo><msup><mfenced separators="|"><mo>?</mo></mfenced><mn>2</mn></msup></mrow></mstyle></math>