Solve and explain if the solution is possible or extraneous

In the diagram, ab is tangent to c, ab = 4 inches, and ad = 2 inches. find the radius of the circle.

What is the angle measure, or angle of depression, between this bird and the bird watcher?

Do one of the following, as appropriate: (a) find the critical value z subscript alpha divided by 2 , (b) find the critical value t subscript alpha divided by 2 . 99%; nequals 17; sigma is unknown; population appears to be normally distributed.