Problem:
Let be a convex hexagon with the following properties.
a. and trisect .
b. and .
c. .
Suppose that quadrilaterals and have area and , respectively. Find the area of quadrilateral .
Problem:
Let be a convex hexagon with the following properties.
a. and trisect .
b. and .
c. .
Suppose that quadrilaterals and have area and , respectively. Find the area of quadrilateral .
Solution:
From conditions (a) and (c), we know that triangles , and are similar to one another, each being twice as large as the preceding one in each dimension. Let and . Then, since the quadrilaterals and are similar to one another, we have . Therefore, .
Let . We know by condition (b) that and . Therefore, triangles and have their three sides parallel to one another, and so must be similar. From this we deduce that the three lines joining the corresponding vertices of the two triangles must meet at a point, i.e., that , , are concurrent. Since and intersect at , the points are collinear. Now, because is a parallelogram, bisects . Therefore, since are collinear, also bisects . So the triangles and have equal area.
Now, since the area of quadrilateral is , the area of triangle is . And since the area of quadrilateral is , the area of triangle is . Therefore, the area of quadrilateral is , as desired.