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Which of the following is not true?
  • a)
    log⁡(1 + z) = z −…..about z = 0
  • b)
    +……about z = 2
  • c)
    =0 where C is the circle |z-1| = 2
  • d)
    has no singularity
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
Which of the following is not true?a)log(1 + z) = z −…..a...
Concept:
Taylor series expansion

Option 1:
The standard expansion of log(1 + z) is given as 

Hence, Option 1 is true
Option 2:
Given complex function is 
→ Let’s Resolve f(z) into partial fractions

For expanding about z = 2, let z – 2 = t ⇒ z = 2 + t


Option 3:
Cauchy’s Integral Formula:
If f(z) is an analytic function within a closed curve and if a is any point within C, then

Residue Theorem:
If f(z) is analytic in a closed curve C except at a finite number of singular points within C, then
⁡f(z)dz = 2πi × [sum of residues at the singualr points with in C]
Formula to find residue:
1. If f(z) has a simple pole at z = a, then

2. If f(z) has a pole of order n at z = a, then

Given complex integral is 
where Cis the circle |z-1| = 2;
Now for the given complex function, the pole is -4 with order 2;
The pole - 4 lies outside the given circle C;
Therefore, no residue inside the circle, hence integration will be zero.
Option 3 is also correct
Option 4:
The given complex function is f(z) = 
In this function, the singularities are z = 0, +i, -i;
Therefore, the given function has 3 singularities...
Option 4 is incorrect
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Most Upvoted Answer
Which of the following is not true?a)log(1 + z) = z −…..a...
Concept:
Taylor series expansion

Option 1:
The standard expansion of log(1 + z) is given as 

Hence, Option 1 is true
Option 2:
Given complex function is 
→ Let’s Resolve f(z) into partial fractions

For expanding about z = 2, let z – 2 = t ⇒ z = 2 + t


Option 3:
Cauchy’s Integral Formula:
If f(z) is an analytic function within a closed curve and if a is any point within C, then

Residue Theorem:
If f(z) is analytic in a closed curve C except at a finite number of singular points within C, then
⁡f(z)dz = 2πi × [sum of residues at the singualr points with in C]
Formula to find residue:
1. If f(z) has a simple pole at z = a, then

2. If f(z) has a pole of order n at z = a, then

Given complex integral is 
where Cis the circle |z-1| = 2;
Now for the given complex function, the pole is -4 with order 2;
The pole - 4 lies outside the given circle C;
Therefore, no residue inside the circle, hence integration will be zero.
Option 3 is also correct
Option 4:
The given complex function is f(z) = 
In this function, the singularities are z = 0, +i, -i;
Therefore, the given function has 3 singularities...
Option 4 is incorrect
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Which of the following is not true?a)log(1 + z) = z −…..about z = 0b)+……about z = 2c)=0 where C is the circle |z-1| = 2d)has no singularityCorrect answer is option 'D'. Can you explain this answer?
Question Description
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