I have som question about sums never done them before, didnīt know where to post it its a analysis course so they cant be to misplaced (i hope). Am I on the right track or doing someting completely wrong? All tips appreciated.. (Clapping)

Write the following using Sigma notation:

2)

3)

then we have

and finaly

4)

Actually what does this mean

n is suppose to be the final value. The exercis said write without Sigma notation. My question is does n=k so its ?