2017 AIME II Problems/Problem 10
Rectangle has side lengths and . Point is the midpoint of , point is the trisection point of closer to , and point is the intersection of and . Point lies on the quadrilateral , and bisects the area of . Find the area of .
Impose a coordinate system on the diagram where point is the origin. Therefore , , , and . Because is a midpoint and is a trisection point, and . The equation for line is and the equation for line is , so their intersection, point , is . Using the shoelace formula on quadrilateral , or drawing diagonal and using , we find that its area is . Therefore the area of triangle is . Using , we get . Simplifying, we get . This means that the x-coordinate of . Since P lies on , you can solve and get that the y-coordinate of is . Therefore the area of is .
Solution 2 (No Coordinates)
Since the problem tells us that segment bisects the area of quadrilateral , let us compute the area of by subtracting the areas of and from rectangle .
To do this, drop altitude onto side and draw a horizontal segment from side to . Since is the midpoint of side , Denote as . Noting that , we can write the statement Using this information, the area of and are and respectively. Thus, the area of quadrilateral is Now, it is clear that point lies on side , so the area of is Given this, drop altitude (let's call it ) onto . Therefore, From here, drop an altitude onto . Recognizing that and that and are similar, we write The area of is given by ~blitzkrieg21 and jdong2006
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