Advanced Math practice question

Answer: −7 or -7

A solution makes the equation true, so substitute x = 3: 9 + 3k + 12 = 0, giving 3k = −21 and k = −7. (Check: x² − 7x + 12 = (x − 3)(x − 4).)

Common wrong answers

If you answered 4

4 is the other solution of the equation, not the value of k.

If you answered 7

A sign slipped: 9 + 12 = 21 must be moved to the other side as −21, so 3k = −21 and k = −7.

If you answered −4

−4 is the negative of the OTHER solution, x = 4. The question asks for k, which is −(3 + 4) = −7.

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