How do you do this question?

C, A, D, B

Step-by-step explanation:

(a) We need to compare the sum of this series to 3/4 and 31/36.  So we just need to find the sum within 1/36.

1 / (n + 1 + 1)² ≤ 1/36

(n + 2)² ≥ 36

n + 2 ≥ 6

n ≥ 4

So we just need to find the partial sum of the terms from n=0 to n=4.

1 − 1/4 + 1/9 − 1/16 + 1/25 ≈ 0.839

We can use this to approximate the actual sum within 1/64.

(b) 1 − 1/7 + 1/49 − 1/343 + ...

We can rearrange this as the difference between two geometric series:

(1 + 1/49 + 1/2401 + ...) − (1/7 + 1/343 + 1/16807)

∑₀°° (1/49)ⁿ − ∑₀°° 1/7 (1/49)ⁿ

1 / (1 − 1/49) − (1/7) / (1 − 1/49)

(6/7) / (48/49)

7/8

So from smallest to largest, the answer is C, A, D, B.

step-by-step explanation: