Series Question Help! (1 Viewer)

[redpint]

hi everyone, how would you do this question?
Evaluate the sum of the first 20 terms of the series
5 - 2 + 10 - 8 + 15 - 32 ...
Thanks!

 

[michaeljennings]

Split this up into an AP and GP
AP: 5, 10, 15 ...
GP: -2, -8, -32 ...

Then evaluate the sum of the first 10 terms for the AP and then the sum of the first 10 terms for the GP and thats the sum of the first 20 terms of your original series