Sequences and series

[IBstudent]

Hello!

Can anyone please help me solve question 15 (c) attached? It's about sequence and series and I tried solving for a while now with no luck....

As you can see I attempted to solve it but I never ended up with a final answer, if someone could help me, I would very much appreciate it

According to the mark scheme, the answer is 7...

 

[IBstudent]

It appears to me that the mark (grade) you were given is 7 out of a possible 11. You answered half of part b incorrectly. You messed up on a decimal point. I can't follow your work on c but you initially set things up properly, and it appears that you were given part credit for doing that. I do not see that you ever gave a numeric answer to part c. I do not know a closed form solution to part c, but it is not hard, particularly with a graphing calculator, to find the numeric answer. Are you asking for a method to find the answer to part c that does not require a graphing calculator?

Actually, 7 was the page number, incidently, it is the answer to part c as well.

I do have a graphing calculator... can you please give me the method in which I can solve this problem using the calculator?

Thanks in advance