Solution 7 (c).

See text and/or instructor's solution manual.

Answer  [Graphics:../Images/CauchyGoursatModHome_gr_347.gif].  

                              [Graphics:../Images/CauchyGoursatModHome_gr_348.gif]

                    The points  [Graphics:../Images/CauchyGoursatModHome_gr_349.gif]  and  [Graphics:../Images/CauchyGoursatModHome_gr_350.gif]  which lie inside the contour  [Graphics:../Images/CauchyGoursatModHome_gr_351.gif].

Solution.  Factor the denominator of the integrand  [Graphics:../Images/CauchyGoursatModHome_gr_352.gif]  to see that  [Graphics:../Images/CauchyGoursatModHome_gr_353.gif].  

The integrand  [Graphics:../Images/CauchyGoursatModHome_gr_354.gif]  is analytic everywhere except at the points  [Graphics:../Images/CauchyGoursatModHome_gr_355.gif]  which lie inside the contour  [Graphics:../Images/CauchyGoursatModHome_gr_356.gif].

Now use partial fractions and express the integrand as  [Graphics:../Images/CauchyGoursatModHome_gr_357.gif],   and split up the integral into two parts

                    [Graphics:../Images/CauchyGoursatModHome_gr_358.gif][Graphics:../Images/CauchyGoursatModHome_gr_359.gif].  

Now use Corollary 6.1 to evaluate the last two integrals:  [Graphics:../Images/CauchyGoursatModHome_gr_360.gif]   and   [Graphics:../Images/CauchyGoursatModHome_gr_361.gif]
                    
Therefore, we have  

                    [Graphics:../Images/CauchyGoursatModHome_gr_362.gif]  

We are done.   

Aside.   In Section 6.5 we will learn to evaluate contour integrals with the Cauchy Integral Formula.  

        The more advanced methods are easier to use but require special attention to details.  

Techniques for evaluating integrals using contours is an important area of complex analysis,

and we will explore this in detail starting with the Residue Calculus in Section 8.1.

        Once the Residue Calculus has been introduced in Section 8.1, computing this integral will be a trivial:

                    [Graphics:../Images/CauchyGoursatModHome_gr_363.gif] .

We are really done.   

Aside.  We can let Mathematica double check our work.

[Graphics:../Images/CauchyGoursatModHome_gr_364.gif]

[Graphics:../Images/CauchyGoursatModHome_gr_365.gif]



[Graphics:../Images/CauchyGoursatModHome_gr_366.gif]

[Graphics:../Images/CauchyGoursatModHome_gr_367.gif]



[Graphics:../Images/CauchyGoursatModHome_gr_368.gif]

[Graphics:../Images/CauchyGoursatModHome_gr_369.gif]



















This solution is complements of the authors.































 

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