Related Rates Problem- Emergency?

Question

I am trying to do the problem below but I don't understand how to do it. Can you please show me how to do it? DON'T give me the answer, explain to me how to get the answer.

Figure: http://img134.imageshack.us/img134/9168/untitled1au7.jpg

Point C moves at a constant rate along semicircle centered at ) from A to B. The radius of the semicircle is 10 cm, and it takes 30 sec for C to move from A to C. Angle COB has measure y radians, angle OCA has measure z radians, and AC = x cm as indicated in the figure.

a) What is the rate of change, in radians per sec, of x with respect to time?

b) What is the rate of change, in radians per sec, of y with respect to time?

c) x and y are related by the Law of Cosines; that is, y^2 = 10^2 + 10^2 - 2(10)(10)cos y. What is the rate of change of x with respect to time when y = π/2 radians?

d) Let D be the area of ΔOAC. Show that D is largest when x = π/2 radians.

Answer 1

^ Parasite alert LOL! ^

30 s for C to move from A to B, maybe? I'll assume that. Also, x seems to be a length, not an angle. Maybe a) is asking for the rate of change of z (called z')? We know the angular rate of C about O (y') is pi/30 (answer to b)), and triangle CAO is isosceles, so z'=-0.5*pi/30.
For c), circumferential velocity is pi*r/30. Angle CAO is, conveniently, 45 deg, so x' = sqrt(0.5)*circumferential velocity.
For d), the area of triangle OAC is .5*AO*altitude, and altitude=r*sin(y). This is a maximum when y (not x) =pi/2.
Sorry, I know you wanted no answers, but I couldn't see how/where to stop short of most of the answers.