Example 8.18.  Evaluate  [Graphics:Images/IntegralsTrigImproperMod_gr_50.gif].  

[Graphics:Images/IntegralsTrigImproperMod_gr_51.gif]

Explore Solution 8.18.

Enter the functions  [Graphics:../Images/IntegralsTrigImproperMod_gr_58.gif]  and  [Graphics:../Images/IntegralsTrigImproperMod_gr_59.gif]  and locate the singularities of  f[z].

[Graphics:../Images/IntegralsTrigImproperMod_gr_60.gif]




[Graphics:../Images/IntegralsTrigImproperMod_gr_61.gif]

 

 

 

Which poles lie in the upper half plane?

[Graphics:../Images/IntegralsTrigImproperMod_gr_62.gif]




[Graphics:../Images/IntegralsTrigImproperMod_gr_63.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_64.gif]

 

 

 

Compute the residues at  [Graphics:../Images/IntegralsTrigImproperMod_gr_65.gif],  and use the residue calculus to compute the value of the integral.

[Graphics:../Images/IntegralsTrigImproperMod_gr_66.gif]





[Graphics:../Images/IntegralsTrigImproperMod_gr_67.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_68.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_69.gif]

 

 

 

Remark.  The integral of  F[x] for this problem is  g[x],  but it cannot be used in any meaningful way to solve the problem at hand.

[Graphics:../Images/IntegralsTrigImproperMod_gr_70.gif]



[Graphics:../Images/IntegralsTrigImproperMod_gr_71.gif]

 

 

 

This looks good, however it cannot be used to solve for the definite integral. This does not agree with the answer obtained with the residue calculus.

[Graphics:../Images/IntegralsTrigImproperMod_gr_72.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_73.gif]

 

 

However, the definite integral will produce the following result.

[Graphics:../Images/IntegralsTrigImproperMod_gr_74.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_75.gif]

 

 

Which is also the correct answer.

The PrincipalValue option can also be used.

[Graphics:../Images/IntegralsTrigImproperMod_gr_76.gif]

[Graphics:../Images/IntegralsTrigImproperMod_gr_77.gif]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) 2006 John H. Mathews, Russell W. Howell