Geometric Sum

The questions below are due on Thursday February 13, 2025; 02:00:00 PM.
 
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Part a. Determine a closed-form expression for the following sum:

S_N=\sum_{n=0}^{N-1}a^n
Hint: Compare S_N to aS_N.

Is your closed-form expression valid for all a and N? If not, determine alternative expressions for these (and any other) edge cases.

Part b. Determine a closed-form expression for the following sum:

S_\infty=\sum_{n=0}^\infty a^n
Is your closed-form expression valid for all a? Explain.

Part c. Determine a closed-form expression for the following sum (with infinitely many terms):

S_d=1+2a+3a^2+4a^3+5a^4+\cdots
Hint: Differentiate.

Is your closed-form expression valid for all a? Explain.


Upload your solution to this problem (including parts a, b, and c) as a single pdf file.
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