Difference between revisions of "1977 AHSME Problems/Problem 21"
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For how many values of the coefficient a do the equations <cmath>\begin{align*}x^2+ax+1=0 \\ x^2-x-a=0\end{align*}</cmath> have a common real solution? | For how many values of the coefficient a do the equations <cmath>\begin{align*}x^2+ax+1=0 \\ x^2-x-a=0\end{align*}</cmath> have a common real solution? | ||
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+ | == See Also == | ||
+ | {{AHSME box|year=1977|num-b=20|num-a=22}} |
Latest revision as of 16:57, 17 December 2024
Problem
For how many values of the coefficient a do the equations have a common real solution?
Solution
Subtracting the equations, we get , or , so or . If , then , which satisfies the condition. If , then is nonreal. This means that is the only number that works, so our answer is .
~alexanderruan
See Also
1977 AHSME (Problems • Answer Key • Resources) | ||
Preceded by Problem 20 |
Followed by Problem 22 | |
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 • 26 • 27 • 28 • 29 • 30 | ||
All AHSME Problems and Solutions |