NECO 2005 Mathematics · Question 34

If x + 1x\frac{1}{x} = 8, find x2^2 + 1x2\frac{1}{x^2}

Options

  1. A.64
  2. B.62
  3. C.32
  4. D.16
  5. E.4

Answer: B. 62

Explanation written with AI and checked against the answer key

Analyze the question: We're given x + 1/x = 8 and asked for x² + 1/x². This is a classic algebra identity question.

Concept: Squaring a sum gives

(x + 1/x)² = x² + 2(x)(1/x) + 1/x² = x² + 2 + 1/x²

The middle term simplifies because x · (1/x) = 1, so it becomes 2.

Solution:

  1. Square both sides of x + 1/x = 8: (x + 1/x)² = 8² x² + 2 + 1/x² = 64
  1. Subtract 2 from both sides: x² + 1/x² = 64 − 2 = 62

Answer: x² + 1/x² = 62, which is option B.

Tip: Whenever you see x + 1/x = k, the answer for x² + 1/x² is always k² − 2. The common mistake is choosing 64 (option A) by forgetting to subtract the 2. Likewise, if you see x − 1/x = k, then x² + 1/x² = k² + 2.

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