In the visual model of the square of a+b, into which parts is the large square divided?

Correct answer: One a² square, one b² square, and two rectangles each with area ab

The direct answer is A. The large square has side a+b. Divide one side into lengths a and b, and do the same to the adjacent side. The partition produces four regions: the a by a corner is a², the b by b corner is b², and the two remaining a by b regions are rectangles with area ab each. Adding them gives a²+ab+ab+b²=a²+2ab+b². Option A lists exactly these four regions. Option B misses one ab rectangle, so it would give the wrong middle term. Option C invents four square regions; the cross-regions are rectangles, not generally squares. Option D has the wrong number of rectangles and therefore cannot represent the four-part division. Memory cue: a square of a sum has two corner squares and two equal cross-rectangles.