I´m sorry I still don´t get how to get the answer

So I have the same issue. I posted 1.5hours ago.

Thank you hallsofIvy but I don´t grasp how to continue.

Sigma from k=1 to n

How on earth do I get that to be ?

I tried this . Then I try to get every term that includes an n to the same denominator. so I get

so I get and ofcourse that is almost very very not right.

So well that didn´t work.

Well I tried the other way that gives me

And that doesn´t help....I really don´t need a complete solution maybe a hint would work wonders....