Radical symmetry trick: If x = 2 + √3, evaluate (√x + 1/√x).

Difficulty: Medium

Correct Answer: √6

Explanation:


Introduction / Context:
Expressions of the form √x + 1/√x can often be evaluated without explicitly finding √x by using the identity (√x + 1/√x)^2 = x + 1/x + 2. The key is to compute x + 1/x first, which is straightforward for numbers of the form a + √b.



Given Data / Assumptions:

  • x = 2 + √3.
  • We need the exact value of √x + 1/√x.
  • x is positive, so √x is real and positive.


Concept / Approach:
Compute 1/x by rationalizing the denominator: 1/(2 + √3) = (2 − √3)/(4 − 3) = 2 − √3. Then add x + 1/x to leverage the square identity to find √x + 1/√x.



Step-by-Step Solution:

Compute 1/x: 1/(2 + √3) = 2 − √3Then x + 1/x = (2 + √3) + (2 − √3) = 4Use the identity: (√x + 1/√x)^2 = x + 1/x + 2 = 4 + 2 = 6Therefore, √x + 1/√x = √6 (positive root because √x is positive)


Verification / Alternative check:
Let t = √x. Then t^2 = x and (t + 1/t)^2 = t^2 + 1/t^2 + 2 = x + 1/x + 2. Plug in the computed value to confirm t + 1/t = √6.



Why Other Options Are Wrong:
√3 and 2 are too small; 2√6 and 6 are too large and come from squaring without taking the square root properly.



Common Pitfalls:
Forgetting to add the extra +2 when using (√x + 1/√x)^2, or rationalizing 1/x incorrectly.



Final Answer:
√6

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