The area of square $ABCD$ is 73 units².

Since the area is between $8^2 = 64$ and $9^2 = 81$, the side length must be between 8 units and 9 units. We can use tracing paper to trace a side length and compare it to the grid, which also shows the side length is between 8 units and 9 units.

When we want to talk about the exact side length, we can use the square root symbol. We say “the square root of 73,” which is written as $\sqrt{73}$ and means “the side length of a square with area 73 square units.” It is also true that $\left( \sqrt{73} \right)^2=73$.