Difference between revisions of "1969 AHSME Problems/Problem 7"

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== Solution ==
 
== Solution ==
<math>\fbox{A}</math>
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Because the two points are on the quadratic, <math>y_1 = a + b + c</math> and <math>y_2 = a - b + c</math>.  Because <math>y_1 - y_2 = -6</math>,
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<cmath>(a+b+c)-(a-b+c)=-6</cmath>
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<cmath>2b=-6</cmath>
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<cmath>b=-3</cmath>
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The answer is <math>\boxed{\textbf{(A)}}</math>.
  
== See also ==
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== See Also ==
 
{{AHSME 35p box|year=1969|num-b=6|num-a=8}}
 
{{AHSME 35p box|year=1969|num-b=6|num-a=8}}
  
 
[[Category: Introductory Algebra Problems]]
 
[[Category: Introductory Algebra Problems]]
 
{{MAA Notice}}
 
{{MAA Notice}}

Latest revision as of 16:01, 20 June 2018

Problem

If the points $(1,y_1)$ and $(-1,y_2)$ lie on the graph of $y=ax^2+bx+c$, and $y_1-y_2=-6$, then $b$ equals:

$\text{(A) } -3\quad \text{(B) } 0\quad \text{(C) } 3\quad \text{(D) } \sqrt{ac}\quad \text{(E) } \frac{a+c}{2}$

Solution

Because the two points are on the quadratic, $y_1 = a + b + c$ and $y_2 = a - b + c$. Because $y_1 - y_2 = -6$, \[(a+b+c)-(a-b+c)=-6\] \[2b=-6\] \[b=-3\] The answer is $\boxed{\textbf{(A)}}$.

See Also

1969 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 6
Followed by
Problem 8
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 31 32 33 34 35
All AHSME Problems and Solutions

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