1956 AMC 12 Problem 15

Attempt Problem 15 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).

15.

The root(s) of 15x2−4−2x−2=1\dfrac{15}{x^2-4}-\dfrac2{x-2}=1 is (are):
−5-5 and 33
±2\pm2
22 only
−3-3 and 55
33 only
Answer: A
Concepts:rational equationfactoringdomain restrictions
Small hint:
The original equation requires x≠±2x\ne\pm2
Big hint:
Multiply through by (x−2)(x+2)(x-2)(x+2) and collect terms
Solution:
For x≠±2,x\ne\pm2, multiplying by x2−4x^2-4 gives 15−2(x+2)=x2−4. 15-2(x+2)=x^2-4. Hence x2+2x−15=0,x^2+2x-15=0, so (x+5)(x−3)=0. (x+5)(x-3)=0. Both x=−5x=-5 and x=3x=3 satisfy the domain restriction.
Thus, the correct answer is A.
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