In which model can \(a^2-2ab+b^2\) be seen?

Correct answer: Square of side \(a-b\)

The direct answer is B: the square with side \(a-b\). The relevant identity is \((a-b)^2=a^2-2ab+b^2\). In a visual interpretation, begin with the large \(a\)-by-\(a\) square, remove two rectangular regions each having area \(ab\), and retain the small \(b\)-by-\(b\) square. The resulting signed area is \(a^2-ab-ab+b^2=a^2-2ab+b^2\). Option A gives \((a+b)^2=a^2+2ab+b^2\), so its middle term is positive. Option C gives \((ab)^2=a^2b^2\), which is not the same expression. Option D gives \((a+b^2)^2", which contains terms such as \(2ab^2\) and \(b^4\). Thus only B has the correct structure and sign. Memory cue: the negative middle term identifies the difference square.