Solution: Using Heron's formula, the semi-perimeter $s = \frac7 + 8 + 92 = 12$. The area is $\sqrt12(12-7)(12-8)(12-9) = \sqrt12 \times 5 \times 4 \times 3 = \sqrt720 = 12\sqrt5$. The inradius $r = \frac\textAreas = \frac12\sqrt512 = \sqrt5$. \boxed\sqrt5 - Nelissen Grade advocaten