NECO 2005 Mathematics · Question 34
If x + = 8, find x +
Options
- A.64
- B.62
- C.32
- D.16
- 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:
- Square both sides of x + 1/x = 8: (x + 1/x)² = 8² x² + 2 + 1/x² = 64
- 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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