ISEE Mathematics Achievement Question 7: Answer and Explanation

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Question: 7

7. If (x + 6)2 = x2 + nx + 36, what is the value of n?

  • A. 3
  • B. 6
  • C. 12
  • D. 36

Correct Answer: C

Explanation:

C

Use FOIL (First, Outside, Inside, Last) on the two factors: (x + 6)(x + 6) = (x2 + 6x + 6x + 36). Combine like terms: x2 + 12x + 36. Thus, n = 12.

Plug in a number for x, such as x = 2, and solve both sides of the equation: 82 = 4 + 2n + 36, so 64 = 40 + 2n. Combine like terms and divide by 2: n = 12.

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