Advanced Math practice question

Answer: 9

A quadratic has exactly one real solution when its discriminant is zero: (−6)² − 4(1)c = 0, so 36 − 4c = 0 and c = 9. (Then the equation is (x − 3)² = 0, with the single solution x = 3.)

Common wrong answers

If you answered 3

3 is the repeated SOLUTION of the equation once c = 9, not the value of c.

If you answered 6

6 is the coefficient of x, not c. The condition is b² − 4ac = 0, which gives 36 = 4c.

If you answered 36

36 is b², one step short. Set 36 − 4c = 0 and solve: c = 9.

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