Trapezoid ABCD, with bases AB and CD, has side lengths AB=28,BC=13,CD=14, and DA=15. Let diagonals AC and BD intersect at P, and let E and F be the midpoints of AP and BP, respectively. Find the area of quadrilateral CDEF.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Note that EF is a midline of triangle APB, so EF is parallel to AB and EF=21AB=14=CD. We also have that EF is parallel to CD, and so CDEF is a parallelogram. From this, we have EP=PC as well, so CACE=32. It follows that the height from C to EF is 32 of the height from C to AB. We can calculate that the height from C to AB is 12 , so the height from C to EF is 8 . Therefore CDEF is a parallelogram with base 14 and height 8 , and its area is 14⋅8=112.
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