2002 AMC 12A Problems/Problem 23
Problem
In triangle , side and the perpendicular bisector of meet in point , and bisects . If and , what is the area of triangle ABD?
Solution
Solution 1 Looking at the triangle , we see that its perpendicular bisector reaches the vertex, therefore hinting it is isoceles. Let , so that from given and the previous deducted. Then because any exterior angle of a triangle has a measure that is the sum of the two interior angles that are not adjacent to the exterior angle. That means and are similar, so .
Then by using Heron's Formula on (with sides ), we have .
Solution 2
Let M be the point of the perpendicular bisector on BC. By the perpendicular bisector theorem, and . Also, by the angle bisector theorem, . Thus, let and . In addition, .
Thus, cos. Additionally, using the Law of Cosines and the fact that , cos
Substituting and simplifying, we get
Thus, . We now know all sides of . Using Heron's Formula on ,
See Also
2002 AMC 12A (Problems • Answer Key • Resources) | |
Preceded by Problem 22 |
Followed by Problem 24 |
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All AMC 12 Problems and Solutions |