Multiple choice

If $4$ is a root of a quadratic equation ${x^2} + ax - 8=0$ then $a=$ _____

  1. $2$
  2. $4$
  3. $-2$
  4. $-4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If 4 is a root, it must satisfy the equation: (4)^2 + a(4) - 8 = 0. 16 + 4a - 8 = 0. 8 + 4a = 0. 4a = -8, so a = -2.

AI explanation

Because 4 is a root of the quadratic equation x^2 + ax - 8 = 0, it must satisfy the equation. Substituting x = 4 into the equation yields (4)^2 + a(4) - 8 = 0, which simplifies to 16 + 4a - 8 = 0 or 4a + 8 = 0. Solving this linear equation for a gives 4a = -8, meaning a = -2.

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