A visual area model for (a − b)² is made by removing two strips of width b from a square of side a. Why is b² added in this model?

Correct answer: The common b² region of the two strips is subtracted twice.

The correct answer is B. Start with the large square of area a². Removing one strip of dimensions a by b removes ab; removing the second strip removes another ab. However, the two strips overlap at the corner in a b by b square, whose area is b². That common corner was included in both removed areas, so it was subtracted twice. To correct the double subtraction, add b² back once: a² − ab − ab + b² = a² − 2ab + b² = (a − b)². A is false because the strips do overlap. C is false because a complete strip has area ab, not b². D is not generally true and does not describe the correction. Memory cue: when two removed regions overlap, add their common part back once.