I have three answers.

This is a B-squared brain turn.

This is a math problem in the lower grades. The picture shows two squares with known side lengths stacked together.

B square -a square

Three. This is the math problem map of senior three students. This is also a picture of two overlapping squares. The length of the big side is called b, and the distance from the big side to the small side is a.

"I" b square -(b-2a) square

2ab+2a(b-2a)

The result is 4ab-4a squared.