Help guys!!

[chilly stratus]

I'm new to sequence and series I have tried this many time but the answer is always one somehow but it is saying the answer is -3/2 how???????

[upper schooner]

For (a) just write these sums for 1, 3, 5 terms. You should get what is going on.

[chilly stratus]

hmmm in this question 1, 3, 5, .. all terms answer are equal right??

[upper schooner]

nope. even terms and odd terms are different

so, for example, for 3 terms you should put n=1,2,3 and add all these together

[chilly stratus]

ahhh i got it