In a square of side (2a+b), how is the (b^2) part formed?

Correct answer: From the square of b

Direct answer: C, from the square of b. A square whose side length is b has area b×b=b². In the larger square with side 2a+b, the b portion on one direction combines with the b portion on the other direction to create the small b-by-b square. Option A gives (2a)b=2ab, which is a rectangular cross-term, not b². Option B gives (2a)²=4a², the square of the other portion. Option D is a sum of lengths, not an area, and it does not produce the term b². A useful rule is that a squared term such as b² comes from a square tile whose two dimensions are both b.