Express the following series as a function of r. a. Note: In the series above, a is the index of the summation. If r is between -1 and 1 (e.g. r < 1 ), the infinite series has a closed form expression. p = 1 +r+r + +.... = 23 Consider the following infinite series. z 1 20 = Hint for part(b): 20 Ir = 1+r+p +3 +... -2-(2) dr Note that we can interchange the order of the summation and differentation if the series is convergent for some values of r. e.g. r < 1. Activat Go to Set if |r| < 1