Which of the following expressions can be factorised using the identity a^2 + 2ab + b^2 = (a + b)^2?

Correct answer: x^2 + 10x + 25

The correct answer is A: x^2 + 10x + 25 = (x + 5)^2. Compare the expression with a^2 + 2ab + b^2. Choose a = x and b = 5. Then a^2 = x^2, 2ab = 2(x)(5) = 10x, and b^2 = 25. Every part matches, so the identity applies directly. Option B has 24 instead of 25, so the last term is not the square of 5. Option C has 5x instead of 10x; the middle term is not twice the product of the two square roots. Option D has a negative middle term and a constant 24, so it matches neither the plus-square nor the minus-square pattern. To avoid confusion, do not check only the first and last terms: always verify the middle term as twice the product of their square roots, with the correct sign.