3. \(\triangle ABC\) 中 I 為內心,內切圓半徑為 r,\(\overline{BC} = a, \overline{CA} = b, \overline{AB} = c, \overline{AI} = x, \overline{BI} = y, \overline{CI} = z, s = \frac{a + b + c}{2}\),試證明:abcr = xyzs。
3. \(\triangle ABC\) 中 I 為內心,內切圓半徑為 r,\(\overline{BC} = a, \overline{CA} = b, \overline{AB} = c, \overline{AI} = x, \overline{BI} = y, \overline{CI} = z, s = \frac{a + b + c}{2}\),試證明:abcr = xyzs。