[填空题]
The following diagram shows part of a circle with cent0bx ,s gsv9yc/:yfei l c5ozs7* yhx(5re O a6lt+xo4zye3; :pa7u gn wdc x1nd radius 5 cm.
Points $\mathrm{A}, \mathrm{B}$ lie on the circle, chord $\mathrm{AB}$ has a length of 8 $\mathrm{~cm}$ and $\mathrm{AO} \mathrm{B}=\theta$ .
1. Find the value of $ \theta$ , giving your answer in radians.≈
2. Find the area of the shaded region.≈ $cm ^2$
