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              Exercise
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1. A trace diagram of a function call illustrates the computational 
   process generated by the function. 

    Review the function trace diagram for (my-sqrt 4).

   Trace Diagram 
   Assume  epsilon = 0.5 and the initial guess = 1.
    (my-sqrt 4)
    (sqrt-iter 4 1)   
    (sqrt-iter 4 2.5)
    (sqrt-iter 4 2.05)
    2.05

   Draw a trace diagram for (my-sqrt 4) with epsilon = 0.01 and the 
   initial guess = 1.

2. Using heron.ss as a model, build cube.ss, that contains the function
   (cbrt x) to compute the cubed root of x.
   
 You should write auxiliary functions that are called within (cbrt x).

   To generate a better guess use the formula:
     

         better-guess(x,g) =  (x/(g*g)) + 2g
                              --------------
                                   3
                             
   * g is the current guess
  




You can test (cbrt x) against the built in function (expt x k).

Here's the contract for expt
;; Number Nubmer -> Number
(expt x k) -> return x to the kth power.

3. Draw a user defined function decomposition diagram for (cbrt x).