2009 AIME I Problems/Problem 4
Problem 4
In parallelogram , point is on so that and point is on so that . Let be the point of intersection of and . Find .
Solution
Solution 1
One of the ways to solve this problem is to make this parallelogram a straight line.
So the whole length of the line ( or ), and is
And ( or ) is
So the answer is
Solution 2
Draw a diagram with all the given points and lines involved. Construct parallel lines and to , where for the lines the endpoints are on and , respectively, and each point refers to an intersection. Also, draw the median of quadrilateral where the points are in order from top to bottom. Clearly, by similar triangles, and . It is not difficult to see that is the center of quadrilateral and thus the midpoint of as well as the midpoint of (all of this is easily proven with symmetry). From more triangle similarity, .
See also
2009 AIME I (Problems • Answer Key • Resources) | ||
Preceded by Problem 3 |
Followed by Problem 5 | |
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All AIME Problems and Solutions |