Advanced Math practice question

Answer: 0

Move everything to one side and factor: x³ − 9x = x(x² − 9) = x(x − 3)(x + 3) = 0. The solutions are 0, 3 and −3, which sum to 0. (Dividing by x would have lost the solution x = 0.)

Common wrong answers

If you answered 3

3 is only the positive solution; −3 and 0 are solutions too.

If you answered 6

6 adds 3 and 3, missing that one root is −3.

If you answered 9

9 is the coefficient in the equation, not a sum of solutions.

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