Application of series! (1 Viewer)

[SGSII]

Hi guys
Could someone please help me do part b) of this question:


Thanks

 

[Capt Rifle]

wouldn't you just need to use the sum formula?

Edit: this n/2(2a+(n-1)d) ??

 

[TheMathStudent]

part b) so the series goes 6+12+18.... use sum formula as above n=k, a=6, d=6
part c) expand the sum formula so that you get k^2 (or n^2 if dealing with just end) and then solve the quadratic. Remember to chuck the negative solution out as n>0