MATHEMATICS · Subjective · AP · Calculus BC · Infinite Sequences and Series · Infinite Sequences and Series
Problem
For the alternating series k=1∑∞(−1)k+1k21, let S denote the exact sum and Sn the sum of its first n terms. Explain in one sentence why ∣S−Sn∣ cannot exceed the magnitude of the (n+1)st term.