Could you tell me the answer of 3(b)? Please

(b)

Step-by-step explanation:

(a)

First, we have to prove that:

Operate:

Simplifying:

(b)

Now we use the above expression to find the sum:

Let's use [1] for each term of the sum:

Substituting:

Note the terms 1/2 and -1/2, 1/3 and -1/3, etc. are canceled out, leaving only the first and last terms:

step-by-step explanation:

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