*  Reading Outline, Sec4.6 *
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* Vocabulary/Definitions *
 - What interpretation of the derivative do we use in this section?
 - How can we sidestep the problem of only knowing a rate at an instant?  
   What derivative short cut then becomes key in our calculation?



* Understand *
1. Suppose that S and x are both functions of t.  If S = 2x^2 +
28/x, find dS/dt.


2. Suppose a drawbridge that is 5 meters long is raised at a constant angular
rate of 0.1 radians/second.  When it is half way up (theta =
pi/4), how fast is the x coordinate of the end of the drawbridge
changing?