If (x + 8)(x + 9) = 0, that means that either x + 8 = 0 or x + 9 = 0.
Solving each equation for x, we find that x = -8 or x = -9.
Write your answer as the set of numbers {-8, -9}.
A common mistake in this problem is for students to see
that (x + 8)(x + 9) = 0 and to say that the answer therefore is 8 or 9.
Note however that the sign of each
number switches in your final answer.