Consider the infinite series sigma ^infinity _k = 1 1/7^k a. Find the first four terms of the sequence of partial sums. b. Use the results of part (a) to propose a formula for S_n. c. Propose a value of the series. a. Find the first four terms of the sequence of partial sums. S_1 =, S_2 =, S_3 =, S_4 = (Simplify your answers.) b. Use the results of part (a) to propose a formula for S_n. A. S_n = 7^n - 1/6 middot 7^n B. S_n = 7n/7^n C. S_n = n/7^n D. S_n = 6 middot 7^n/7^n - 1 c. Propose a value of the series. A reasonable conjecture for the value of the series is