Q18Multiple choiceSquare of 9x – 7xy is(a)81x2 + 49x2y2(b)81x2 – 49x2y2(c)81x2 + 49x2y2 –126x2y(d)81x2 + 49x2y2 – 63x2yShow answer(c) 81x2 + 49x2y2 –126x2y