The Student Room Group

complex analysis

question on uniqueness theorem:

let f be an entire function s.t

f(i/n)=cos(1/n) for n a positive integer

show f(z)=cosh (z)

done this by considering S={i/n for n positive integer} noting both f and cosh agree on S and S has limit point.

the next part is

ii) find an entire function f other than f(z)=cosh(z)) that satisfies

f(in)=cos n for n a positive integer

can I just put something like

f(z)=sin(2(pi)z/i) + cos (z/i)? is there any deep justification for any function apart from cosh(z)?

can someone explain how the uniqueness theorem fails on part(ii)

thanks
Reply 1
Original post by mathz
question on uniqueness theorem:

let f be an entire function s.t

f(i/n)=cos(1/n) for n a positive integer

show f(z)=cosh (z)

done this by considering S={i/n for n positive integer} noting both f and cosh agree on S and S has limit point.

the next part is

ii) find an entire function f other than f(z)=cosh(z)) that satisfies

f(in)=cos n for n a positive integer

can I just put something like

f(z)=sin(2(pi)z/i) + cos (z/i)? is there any deep justification for any function apart from cosh(z)?

can someone explain how the uniqueness theorem fails on part(ii)

thanks


Your answer seems fine for the second part

The uniqueness theorem doesn't apply as the points don't have a limit point in this case.

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