3,6,9,12

can u explain plzz

- December 3rd 2008, 05:56 AMNeedHelp18Find the sum of the first 20 terms of this geometric sequence
3,6,9,12

can u explain plzz - December 3rd 2008, 06:03 AMSoroban
Hello, NeedHelp18!

Quote:

Find the sum of the first 20 terms of this geometric sequence:

. . 3, 6, 9, 12, . . .

can u explain plzz

This will take a**lot**of explaining because . . .

(1) You seem to know nothing about sequences . . .

. . .especially the sum-formulas.

(2) It is**not**a geometric sequence.

- December 3rd 2008, 06:38 AMNeedHelp18
is this right?

Sn = (n/2)(a1 + an)

S20 =(10)(3 + 60)

= 630 - December 3rd 2008, 06:42 AMChop Suey