Difference between revisions of "2009 AMC 10B Problems/Problem 12"
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Revision as of 10:38, 13 August 2014
Problem
Distinct points 
, 
, 
, and 
lie on a line, with 
. Points 
and 
lie on a second line, parallel to the first, with 
. A triangle with positive area has three of the six points as its vertices. How many possible values are there for the area of the triangle?
Solution
Consider the classical formula for triangle area: 
.
Each of the triangles that we can make has exactly one side lying on one of the two parallel lines. If we pick this side to be the base, the height will always be the same - it will be the distance between the two lines.
Hence each area is uniquely determined by the length of the base. And it can easily be seen, that the only possible base lengths are 
, 
, and 
. Therefore there are only 
possible values for the area.
(To be more precise in the last step, the possible base lengths are 
, 
, and 
.)
See Also
| 2009 AMC 10B (Problems • Answer Key • Resources) | ||
| Preceded by Problem 11 |
Followed by Problem 13 | |
| 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 | ||
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
