[问答题]
The diagram below shows two ci
jc,7+d,dv7 y . p dztpnyye4-v m yfkt+:tb*z+a5hm ;yrcles with centres at the points A and B and radii 3r and 2r, respectively. The point
mz;k+: b tmyh*fyt+a5 B lies on the circle with centre A. The circles intersect at the points C and D.
Let $\alpha$ be the measure of the angle CAD and $\theta $ be the measure of the angle CBD in radians.
1. Find an expression for the shaded area in terms of $ \alpha, \theta$ and r .
2. Show that $ \alpha=4 \arcsin \frac{1}{3}$ .
3. Hence find the value of r given that the shaded area is equal to 16 $\mathrm{~cm}^{2}$ .
