Difference between revisions of "2002 AMC 10B Problems/Problem 10"

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== Solution ==
 
== Solution ==
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From [[Vieta's Formulas]], <math>ab=b</math> and <math>a+b=-a</math>. Since <math>b\ne 0</math>, we have <math>a=1</math>, and hence <math>b=-2</math>. Our answer is <math>\boxed{(1,-2)\Rightarrow\text{(C)}}</math>.
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==See Also==
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{{AMC10 box|year=2002|ab=B|num-b=9|num-a=11}}
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[[Category:Introductory Algebra Problems]]

Revision as of 14:11, 27 December 2008

Problem

Suppose that $a$ and $b$ are nonzero real numbers, and that the equation $x^2+ax+b=0$ has positive solutions $a$ and $b$. Then the pair $(a,b)$ is

$\mathrm{(A) \ } (-2,1)\qquad \mathrm{(B) \ } (-1,2)\qquad \mathrm{(C) \ } (1,-2)\qquad \mathrm{(D) \ } (2,-1)\qquad \mathrm{(E) \ } (4,4)$

Solution

From Vieta's Formulas, $ab=b$ and $a+b=-a$. Since $b\ne 0$, we have $a=1$, and hence $b=-2$. Our answer is $\boxed{(1,-2)\Rightarrow\text{(C)}}$.

See Also

2002 AMC 10B (ProblemsAnswer KeyResources)
Preceded by
Problem 9
Followed by
Problem 11
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AMC 10 Problems and Solutions