Let ABCD be a parallelogram with AB=8,AD=11, and ∠BAD=60∘. Let X be on segment CD with CX/XD=1/3 and Y be on segment AD with AY/YD=1/2. Let Z be on segment AB such that AX,BY, and DZ are concurrent. Determine the area of triangle XYZ.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Let AX and BD meet at P. We have DP/PB=DX/AB=3/4. Now, applying Ceva's Theorem in triangle ABD, we see that ZBAZ=PBDP⋅YDAY=43⋅21=83 Now, [ABCD][AYZ]=2[ABD][AYZ]=21⋅31⋅113=221 and similarly [ABCD][DYX]=21⋅32⋅43=41 Also, [ABCD][XCBZ]=21(41+118)=8843 The area of XYZ is the rest of the fraction of the area of ABCD not covered by the three above polygons, which by a straightforward calculation 19/88 the area of ABCD, so our answer is 8⋅11⋅sin60∘⋅8819=2193
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