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Show f(z) = √|xy| is not analytic at origin although the C-R equations are satisfied at that point.
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Complex Analysis Theorem from Analytic function
Statement/Theorem /Prove that :-
Show that the function f(z) = sqrt(|xy|) or √|xy| is not analytic at the origin although the Cauchy-Riemann equations are satisfied at that point.
Solution.
Let f(z) = u(x, y) + iv(x, y) =√|xy|
Here
u(x,y)= √|xy| and v(x,y)=0
At the origin zₒ=(0,0),
(∂u/∂x) = lim ₓ→ₒ {u(x, 0) - u(0, 0)}/x
⇒ (∂u/∂x)= (0 - 0)/x
⇒(∂u/∂x) = 0
and
(∂v/∂y) = lim ᵧ→ₒ {v(0, y) - v(0, 0)}/y
⇒(∂v/∂y)= (0 - 0)/y
⇒(∂v/∂y) = 0
Here ,
∵(∂u/∂x) = 0 and (∂v/∂y) = 0
∴(∂u/∂x) = (∂v/∂y)
Hence Cauchy-Riemann equations are satisfied at the origin zₒ=(0,0).
Now by property of differentiability...
f'(0)=lim z→o {f(z)-f(0)}/z
⇒f'(0)=lim z→o {√|xy|-0}/(x+iy)
⇒f'(0)=lim z→o √|xy|/(x+iy)
Now let a line y=mx, z→o we get
⇒f'(0)=lim z→o √|mx²|/(x+imx)
Simplify
⇒f'(0)=lim z→o √|m|/(1+im)
Here f'(0) is dependent on slop m thus the limit is not unique
∴ differentiability is not exist so that f(z) is not Analytic function at the origin zₒ=(0,0).
Hence Proved...!!!
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Statement/Theorem /Prove that :-
Show that the function f(z) = sqrt(|xy|) or √|xy| is not analytic at the origin although the Cauchy-Riemann equations are satisfied at that point.
Solution.
Let f(z) = u(x, y) + iv(x, y) =√|xy|
Here
u(x,y)= √|xy| and v(x,y)=0
At the origin zₒ=(0,0),
(∂u/∂x) = lim ₓ→ₒ {u(x, 0) - u(0, 0)}/x
⇒ (∂u/∂x)= (0 - 0)/x
⇒(∂u/∂x) = 0
and
(∂v/∂y) = lim ᵧ→ₒ {v(0, y) - v(0, 0)}/y
⇒(∂v/∂y)= (0 - 0)/y
⇒(∂v/∂y) = 0
Here ,
∵(∂u/∂x) = 0 and (∂v/∂y) = 0
∴(∂u/∂x) = (∂v/∂y)
Hence Cauchy-Riemann equations are satisfied at the origin zₒ=(0,0).
Now by property of differentiability...
f'(0)=lim z→o {f(z)-f(0)}/z
⇒f'(0)=lim z→o {√|xy|-0}/(x+iy)
⇒f'(0)=lim z→o √|xy|/(x+iy)
Now let a line y=mx, z→o we get
⇒f'(0)=lim z→o √|mx²|/(x+imx)
Simplify
⇒f'(0)=lim z→o √|m|/(1+im)
Here f'(0) is dependent on slop m thus the limit is not unique
∴ differentiability is not exist so that f(z) is not Analytic function at the origin zₒ=(0,0).
Hence Proved...!!!
.
.
.
.
.
.
.
.
Kindly join us for CSIR-UGC National Eligibility Test (NET) for Junior Research Fellowship and Lecturer-ship COMMON SYLLABUS FOR PART 'B' AND 'C' MATHEMATICAL SCIENCE
.
.
.
.
.
All BSc, B.Tech, MSc, MA Mathematics students join with us A great platform to get knowledge in Mathematics and science... Stay tuned....for detailed videos on whole SYLLABUS with topic wise...
.
.
.
.
.
.
.
#complexanalysis #csirnet #analyticfunction
.
Videos links 🔥🔥🔥
Play List ( Complex Analysis)
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