1956 AMC 12 Problem 12

Attempt Problem 12 of the 1956 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1956 AMC 12 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

12.

If x−1−1x^{-1}-1 is divided by x−1x-1 the quotient is:
11
1x−1\dfrac1{x-1}
−1x−1-\dfrac1{x-1}
1x\dfrac1x
−1x-\dfrac1x
Answer: E
Concepts:negative exponentsrational expressionsfactoring
Small hint:
Rewrite x−1−1x^{-1}-1 as 1x−1\frac{1}{x}-1
Big hint:
Factor 1−x=−(x−1)1-x=-(x-1)
Solution:
Where the quotient is defined, x−1−1x−1=1−xxx−1=−(x−1)x(x−1)=−1x. \begin{aligned} \frac{x^{-1}-1}{x-1} &=\frac{\frac{1-x}{x}}{x-1}\\ &=\frac{-(x-1)}{x(x-1)}\\ &=-\frac1x. \end{aligned}
Thus, the correct answer is E.
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