We need to examine 72 and find the highest square number that divides into 72. (Squares are the numbers 12 = 1,   22 = 4,   32 = 9,   42 = 16, ...)

In this case, 36 is the highest square that divides into 72 evenly. We express 72 as 36 × 2 and proceed as follows.

math expression

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