- #1
Pouyan
- 103
- 8
Consider the principal branch of the function
f(z)= z7/3
Find f'(-i) and write it in the form a+bi
My attemp is :
I know zc = exp(c logz)
and the derivative of that is : (c/z) * exp(c Logz)
That is in this case (7/3)*(i) *exp((7/3)*Log-i) = f'(-i)
I know that Log(-i) = Log(1) + i(-pi/2)= -i pi/2
and exp((7/3)(-i pi/2)) = (cos(7pi/6)-i*sin(7pi/6))
and I get (7/3)*(i)(cos(7pi/6)-i*sin(7pi/6)) as final answer
But I see the answer is : -(7/6)(1+isqrt(3))!
What is wrong with my algorithm ?
f(z)= z7/3
Find f'(-i) and write it in the form a+bi
My attemp is :
I know zc = exp(c logz)
and the derivative of that is : (c/z) * exp(c Logz)
That is in this case (7/3)*(i) *exp((7/3)*Log-i) = f'(-i)
I know that Log(-i) = Log(1) + i(-pi/2)= -i pi/2
and exp((7/3)(-i pi/2)) = (cos(7pi/6)-i*sin(7pi/6))
and I get (7/3)*(i)(cos(7pi/6)-i*sin(7pi/6)) as final answer
But I see the answer is : -(7/6)(1+isqrt(3))!
What is wrong with my algorithm ?
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