Difficulty: Easy
Correct Answer: 34
Explanation:
Introduction / Context:
This problem tests an algebraic identity technique: using (x + 1/x)^2 to quickly obtain x^2 + 1/x^2. This avoids solving a quadratic for x and is a common simplification shortcut in aptitude and algebra questions.
Given Data / Assumptions:
Concept / Approach:
Square the given expression. The identity is:\n(x + 1/x)^2 = x^2 + 2 + 1/x^2.\nThen rearrange to isolate x^2 + 1/x^2. This works because the cross term is always 2 when multiplying x by 1/x.
Step-by-Step Solution:
Given: x + 1/x = 6
Square both sides: (x + 1/x)^2 = 6^2
Left side expansion: (x + 1/x)^2 = x^2 + 2*(x*(1/x)) + 1/x^2
Since x*(1/x) = 1, the middle term becomes 2
So: x^2 + 2 + 1/x^2 = 36
Rearrange: x^2 + 1/x^2 = 36 - 2 = 34
Verification / Alternative check:
If desired, you could solve x + 1/x = 6 => x^2 - 6x + 1 = 0 and use the solutions. Both solutions will produce the same value for x^2 + 1/x^2, confirming the identity-based result.
Why Other Options Are Wrong:
36 is the value of (x + 1/x)^2, not x^2 + 1/x^2.
32 is a common mistake from subtracting 4 instead of 2.
23 and 16 do not match the correct rearrangement and are inconsistent with the squared identity.
Common Pitfalls:
Forgetting the cross term 2, or incorrectly writing (x + 1/x)^2 = x^2 + 1/x^2. Another mistake is treating x*(1/x) as x rather than 1.
Final Answer:
x^2 + 1/x^2 = 34
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