17. As shown in the figure, triangle $\mathrm{AED}$ is a right triangle, with the lengths of the two legs being $\mathrm{AE}=15, \mathrm{DE}=20$. A square $A B C D$ is constructed with $A D$ as one side, and a parallelogram $A B F E$ is constructed with $A B, A E$ as sides. $E F$ intersects side $A D$ at point $G$, and $A C$ intersects $\mathrm{FG}$ at point $\mathrm{H}$. The difference in area (larger area minus smaller area) between triangle $\mathrm{AGH}$ and triangle $\mathrm{CFH}$ is $\qquad$
【Analysis】By the Pythagorean theorem, we can calculate: $\mathrm{AD}=25$, so the side length of the square is 25. According to the area of triangle $\mathrm{ADE}$, we can calculate $\mathrm{EG}=12$, so $\mathrm{GF}=13$. Using the Pythagorean theorem in $\mathrm{AEG}$, we get $\mathrm{AG}=9, \mathrm{GD}=16$. The area of triangle $\mathrm{ADC}=25 \times 25 \div 2=312.5$, and the area of trapezoid $\mathrm{CDGF}=(13+25) \times 16 \div 2=304$; the difference in area between triangle $\mathrm{AGH}$ and triangle $\mathrm{CFH}$ = area of triangle $\mathrm{ADC}$ - area of trapezoid $\mathrm{CDGF}=312.5-304=8.5$.