Using the results from problem 1.54, evaluate each of the following sums and express you...

Using the results from problem 1.54, evaluate each of the following sums and express your answer in Cartesian (rectangular) form:

Reference:

The relations considered in this problem are used on many occasions throughout the book.

(a) Prove the validity of the following expression:

This is often referred to as the finite sum formula.

(b) Show that if

This is often referred to as the infinite sum formula.

(c) Show also if

(d) Evaluate