Pendulum - find maximum angular displacement

[Lunadora]

Homework Statement

A 15-centimeter pendulum moves according to the equation:

theta=0.2cos8t

where theta is the angular displacement from the vertical in radians and t is the time in seconds. Determine the maximum angular displacement and the rate of change of theta when t=3 seconds.

Homework Equations

See, here's where I get stuck. It doesn't seem like I'm given enough information to do ANYTHING with this problem. At first I thought I could find the absolute maximum value by solving for theta at the endpoints and critical numbers, but I don't have any endpoints. Any physics equations I could use go out the window as well, because I have no initial displacement or velocity or any such stuff.

The Attempt at a Solution

Insert an hour of frustrated grumbling here, with no results.

 

[Delphi51]

Graph y=0.2cos8t to see the whole picture!
Or recall what value(s) of x make cos x a maximum. Graph y = cos x if you don't recall.