16x² + 24x + 9 can be written as:

Correct answer: (4x + 3)². 16x² + 24x + 9 = (4x)² + 2(4x)(3) + 3² = (4x + 3)².

Background: It is a perfect square trinomial of the form a² + 2ab + b².

• 4x − 3: 4x − 3 is not a square form.
• 4x + 3: 4x + 3 is only the base, not the square.
• (4x + 6)²: (4x + 6)² would expand to 16x² + 48x + 36.

Did you know? The middle term 24x = 2 × 4x × 3 matches.

Memory trick: a² + 2ab + b² = (a + b)².