1985 AIME Problems/Problem 6
Contents
[hide]Problem
As shown in the figure, triangle is divided into six smaller triangles by lines drawn from the vertices through a common interior point. The areas of four of these triangles are as indicated. Find the area of triangle .
Solution
Let the interior point be , let the points on , and be , and , respectively. Let be the area of and be the area of . Note that and share the same altitude from , so the ratio of their areas is the same as the ratio of their bases. Similarly, and share the same altitude from , so the ratio of their areas is the same as the ratio of their bases. Moreover, the two pairs of bases are actually the same, and thus in the same ratio. As a result, we have: or equivalently and so .
Applying identical reasoning to the triangles with bases and , we get so that and . Substituting from this equation into the previous one gives , from which we get and so the area of is .
Solution 2
This problem can be done using mass points as well. Assign B a weight of 1 and realize that many of the triangles have the same altitude. After continuously using the formulas where the sum of the two weights = the middle weight and the the weight times side = other weight times other side, the problem can be trivialized giving the answer
Solution by carlos8
See also
1985 AIME (Problems • Answer Key • Resources) | ||
Preceded by Problem 5 |
Followed by Problem 7 | |
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