2003 AMC 10A Problems/Problem 18

Problem

What is the sum of the reciprocals of the roots of the equation $\frac{2003}{2004}x+1+\frac{1}{x}=0$ ?

$\mathrm{(A) \ } -\frac{2004}{2003}\qquad \mathrm{(B) \ } -1\qquad \mathrm{(C) \ } \frac{2003}{2004}\qquad \mathrm{(D) \ } 1\qquad \mathrm{(E) \ } \frac{2004}{2003}$

Solution 1

Multiplying both sides by $x$ :

$\frac{2003}{2004}x^{2}+1x+1=0$

Let the roots be $a$ and $b$ .

The problem is asking for $\frac{1}{a}+\frac{1}{b}= \frac{a+b}{ab}$

By Vieta's formulas:

$a+b=(-1)^{1}\frac{1}{\frac{2003}{2004}}=-\frac{2004}{2003}$

$ab=(-1)^{2}\frac{1}{\frac{2003}{2004}}=\frac{2004}{2003}$

So the answer is $\frac{a+b}{ab}=\frac{-\frac{2004}{2003}}{\frac{2004}{2003}}=-1 \Rightarrow\boxed{\mathrm{(B)}\ -1}$ .

Solution 2

Dividing both sides by $x$ ,

$\frac{2003}{2004}+\frac 1x+\frac{1}{x^2}=0$ ,

we see by Vieta's formulas(with the same reasoning as above) that the sum of the roots is $-1 \Rightarrow\boxed{\mathrm{(B)}\ -1}$ .

2003 AMC 10A (Problems • Answer Key • Resources)
Preceded by Problem 17	Followed by Problem 19
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2003 AMC 10A Problems/Problem 18

Contents

Problem

Solution 1

Solution 2

See Also