If x + 1/x = 2 (with x ≠ 0), compute the value of x − 1/x. Justify your reasoning clearly.

Difficulty: Easy

Correct Answer: 0

Explanation:


Introduction / Context:
This is a quick identity-based question. When x + 1/x equals a particular constant, it often pins down x uniquely (for reals), enabling immediate evaluation of related expressions like x − 1/x without heavy algebra.


Given Data / Assumptions:

  • x + 1/x = 2.
  • x ≠ 0.


Concept / Approach:
Observe that among real numbers, x + 1/x ≥ 2 with equality if and only if x = 1 (by AM ≥ GM or by completing the square). Thus x must be 1. Then compute x − 1/x directly. Alternatively, square x − 1/x and use the identity (x − 1/x)^2 = (x + 1/x)^2 − 4 to reach the same result.


Step-by-Step Solution:
Since x + 1/x = 2, for real x we get x = 1.Hence x − 1/x = 1 − 1 = 0.Identity check: (x − 1/x)^2 = (2)^2 − 4 = 0 ⇒ x − 1/x = 0.


Verification / Alternative check:
Plug x = 1 back into x + 1/x to verify it equals 2; then x − 1/x clearly vanishes.


Why Other Options Are Wrong:

  • 1, 2, −2, −1: These disregard the equality case of the AM ≥ GM condition or misuse the identity for (x − 1/x)^2.


Common Pitfalls:
Assuming multiple real solutions; forgetting that the minimum value of x + 1/x for real x is 2 at x = 1.


Final Answer:
0

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