1957 AMC 12 Problem 27

Attempt Problem 27 of the 1957 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 1957 AMC 12 solutions, or check the answer key.

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

27.

The sum of the reciprocals of the roots of the equation x2+px+q=0x^2+px+q=0 is:
−pq-\dfrac pq
qp\dfrac qp
pq\dfrac pq
−qp-\dfrac qp
pqpq
Answer: A
Concepts:Vieta’s Formulasrational equation
Small hint:
Call the roots rr and ss, and combine 1r+1s\frac{1}{r}+\frac{1}{s}
Big hint:
Use r+s=−pr+s=-p and rs=qrs=q
Solution:
If the roots are r,s,r,s, then Vieta’s formulas give r+s=−pr+s=-p and rs=q.rs=q. Therefore 1r+1s=r+srs=−pq. \frac1r+\frac1s=\frac{r+s}{rs}=-\frac pq.
Thus, the correct answer is A.
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