Here’s one for the mathematics geeks.

The Author is making a visual pun on the similarity between the square root operator and the division operator. If you follow from left to right you will see the “three times the square root of 81” turn into “81 divided by three” when he drops the multiplication operator. In this particular example, the two numbers multiplied is the same as dividing the second number squared by the first number. This is not always the case.