Exercise 13.  From Exercise 12 and basic cancellation laws, it follows that  .  
The numerator here,  ,  is trivial to calculate and, as the denominator     is a real number (see Exercise 3), computing the quotient    should be rather straightforward.  
Use this fact to compute    if    and again if  .

Solution 13.

See text and/or instructor's solution manual.

For ,  

          

For ,  

          

Aside.  We can let Mathematica double check our work.

and

This solution is complements of the authors.

(c) 2008 John H. Mathews, Russell W. Howell