which of the following is not a characteristic function?
a) 1
b) $e^{it} $ , $t \in R$
c) $\frac{1}{1-it} $, $t\in R$
d)$e^{|-t|}$, $t \in R$
which of the following is not a characteristic function?
a) 1
b) $e^{it} $ , $t \in R$
c) $\frac{1}{1-it} $, $t\in R$
d)$e^{|-t|}$, $t \in R$