if the nth partial sum of a sequence a_n is given by 2k+4 then what is the nth term of the sequence?
A. 2n+4
B. 6+8+10+12...+(2n+4)

Also, http://answers.yahoo.com/question/index?qid=20100105133119AAAp6Hh how do you derive the last term?

Question

if the nth partial sum of a sequence a_n is given by 2k+4 then what is the nth term of the sequence? 
A. 2n+4
B. 6+8+10+12...+(2n+4)

Also, http://answers.yahoo.com/question/index?qid=20100105133119AAAp6Hh how do you derive the last term?

anonymous · Answer

$$a _{n}=S _{n}-S _{n-1}$$

hartnn · Answer

last term an = a1+(n-1) d 
sum = n/2(2a+(n-1)d)

anonymous · Answer

Oh, thanks for that hartnn. Not sure what you were getting at Jonask o.o

anonymous · Answer

@hartnn  that work for all sequences?

anonymous · Answer

$$a _{n}=2n+4-(2(n-1)+4)=2$$y
ou can also find
$$S _{1},S _{2},S _{3}...$$

anonymous · Answer

is that the formula for the nth sum

hartnn · Answer

this clearly seems AP

anonymous · Answer

AP?

anonymous · Answer

Why was the multiple choice A instead of B? Anyone know? I think it has something to do with partial sum

hartnn · Answer

arithmetic progression, sequence.....u know what it is ?

anonymous · Answer

Yes, I do. Just don't link AP with arithmetic progression :)

anonymous · Answer

@hartnn  every sequence = arithmetic sequence.
verify

anonymous · Answer

Does anyone know why it was A instead of B though?

hartnn · Answer

i said this is AP based on the n'th term... of the form a+(n-1)d.

anonymous · Answer

Only things that add or minus in constant intervals are arithmetic sequence