Exercise 9.  Show that the following functions are entire (see Definition 3.2).  

9 (b).  [Graphics:Images/CauchyRiemannModHome_gr_520.gif].  

Solution 9 (b).

See text and/or instructor's solution manual.

Answer.  [Graphics:../Images/CauchyRiemannModHome_gr_521.gif]  and  [Graphics:../Images/CauchyRiemannModHome_gr_522.gif].  

The partials are continuous everywhere, so  g(z)  is entire.

Solution.  [Graphics:../Images/CauchyRiemannModHome_gr_523.gif],    and  

                 [Graphics:../Images/CauchyRiemannModHome_gr_524.gif],      [Graphics:../Images/CauchyRiemannModHome_gr_525.gif]    so that  

[Graphics:../Images/CauchyRiemannModHome_gr_526.gif],     [Graphics:../Images/CauchyRiemannModHome_gr_527.gif],     [Graphics:../Images/CauchyRiemannModHome_gr_528.gif],     [Graphics:../Images/CauchyRiemannModHome_gr_529.gif].   

The  Cauchy Riemann equations are  

        [Graphics:../Images/CauchyRiemannModHome_gr_530.gif],  

        [Graphics:../Images/CauchyRiemannModHome_gr_531.gif],

which hold for all  z.

The partials are continuous everywhere, so   

[Graphics:../Images/CauchyRiemannModHome_gr_532.gif][Graphics:../Images/CauchyRiemannModHome_gr_533.gif],  

for all  z.  Therefore,   [Graphics:../Images/CauchyRiemannModHome_gr_534.gif]  is an entire function.

We are done.   

Remark.  Later, in Section 5.4 we will show that  

(5-34)                    [Graphics:../Images/CauchyRiemannModHome_gr_535.gif],
                    and
(5-35)                    [Graphics:../Images/CauchyRiemannModHome_gr_536.gif].  

Then  [Graphics:../Images/CauchyRiemannModHome_gr_537.gif][Graphics:../Images/CauchyRiemannModHome_gr_538.gif]  will be an analytic function and its derivative is

[Graphics:../Images/CauchyRiemannModHome_gr_539.gif][Graphics:../Images/CauchyRiemannModHome_gr_540.gif].  

We are really done.   

Aside.  We can let Mathematica double check our work.

[Graphics:../Images/CauchyRiemannModHome_gr_541.gif]

[Graphics:../Images/CauchyRiemannModHome_gr_542.gif]
[Graphics:../Images/CauchyRiemannModHome_gr_543.gif]

                     [Graphics:../Images/CauchyRiemannModHome_gr_544.gif]          [Graphics:../Images/CauchyRiemannModHome_gr_545.gif]

  

                    The analytic function  [Graphics:../Images/CauchyRiemannModHome_gr_546.gif]  maps this orthogonal grid onto an orthogonal grid.

 

                    Can you find the subtle difference between the above graphs and those in Exercise 9 (a) ?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This solution is complements of the authors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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