For what value of m is −3 a zero of the polynomial x² − 2x − (m + 3)?

Correct answer: 12. Substituting x = −3 gives 9 + 6 − (m + 3) = 0, so 15 − m − 3 = 0 and m = 12.

Background: A zero of a polynomial is a value of x that makes the polynomial equal to 0.

• 9: m = 9 does not make the polynomial zero at x = −3.
• 15: m = 15 does not make the polynomial zero at x = −3.
• 19: m = 19 does not make the polynomial zero at x = −3.

Did you know? Check: (−3)² − 2(−3) − 15 = 9 + 6 − 15 = 0.

Memory trick: Zero → plug in and solve.