Consider this famous question on real analysis. The function \(f(x)=x\sin(\pi/x)\) for \(x>0\) satisfying Rolle’s theorem for any interval \((1/n,1/(n+1)),n \in \mathbb{N}\). The discussion leads to finding the solutions \(\pm x_1, \pm x_2 , \cdots\) of the equation \(\tan(/pi/x)=\pi/x\) where \(\frac{1}{k+1/2}<x<\frac{1}{k}\) . Show that this equation has no other solution in the complex plane. Hence find the sum of the series \(\sum_{k=1}^\infty z_k^{-2}\) .

Compare the function 

\(\Gamma(z)=\frac{e^{-\gamma z}}{z} \prod_{n=1}^\infty \left(\frac{n}{n+z} \right) e^{z/n}\)

with the canonical theorem of entire functions and provide the inference.

Prove that the function 

\(\Gamma(z)=\frac{e^{-\gamma z}}{z} \prod_{n=1}^\infty \left(\frac{n}{n+z} \right) e^{z/n}\)

is logarithmically convex.

Evaluate the integral \(\int_\gamma \frac{dz}{z^2 +1}\) where \(\gamma(\theta) =2|\cos2\theta|e^{i\theta}\) for \(0\le \theta \le 2\pi\).

Let \(G = \mathbb{C} \backslash\{a,b\},a \neq b \) and \(\gamma\) be the curve in the figure below Show that \(n(\gamma;a) = n(\gamma ;b)\) 

Find all possible values of \(\int_\gamma \frac{dz}{1+z^2}\) where \(\gamma\) is any closed rectifiable curve in \(\mathbb{C}\) not passing through \(\pm i\).

Evaluate \(\int_\gamma \frac{e^z -e^{-z}}{z^4}dz\) where \(\gamma\) is one of the following curves.

Let \(\alpha(t)=e^{it}\) and \(\beta(t)=(3/2)+ 3e^{it}\) for \(t\) in the interval \([0,2\pi]\). Show that \(\alpha\) and \(\beta\) are freely homotopic on \(A=\mathbb{C}\backslash\{0\}\).

Note: Homotopy means deforming one path to another. Freely homotopic means defining a function involving both the paths, as given in the definition of homotopy.

Let \(\alpha:[a,b] \mapsto A\) and \(\beta :[a,b] \mapsto B\) are closed paths in a set \(A\) that is starlike with respect to a point \(z_0\). Show that \(\alpha\) and \(\beta\) are freely homotopic in \(A\) .

Prove that

\(u_c(t) = \left\{ \begin{array} 00 \ for \ 0 \le t \le c, \\ (t-3)^3, \ for \ c\le t < \infty , c>0, \end{array}\right.\)

 is a solution of  \(u^\prime = 3u^{2/3},u(0)=0 .\)

(a) Show that all the solutions of the linear equation \(u^\prime +a(t)u = 0, \ t \in [0,\infty)\), where \(a:[0,\infty) \rightarrow [0,\infty)\) is a continuous function, are always bounded if \(\int_0^\infty a(s)ds < \infty \) .

(b) Consider the equation \((1+t)^2u^\prime - u = 0, \ t \in [0,\infty)\) .

(i) Find the unique solution.

(ii) Show that \(\mid u(0) \mid \le \mid u(t) \mid < \mid u(0) \mid e \), for all \(t \in [0 ,\infty)\) . How you are connecting this result with the problem \((2) (a)\) ?