Factorise x squared - 9 completely.

Answer and explanation

Correct answer: D. (x - 3)(x + 3)

  1. Step 1: Write 9 as 3 squared: x squared - 3 squared. Step 2. Use a squared - b squared = (a - b)(a + b). Answer: (x - 3)(x + 3). Why not the others: (x - 3)(x - 3) expands to x squared - 6x + 9; (x - 9)(x + 1) gives a middle term of -8x; x(x - 9) removes only one x and loses the constant.

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