an = 5 d = -2 n = 12
Last edited by mr fantastic; Sep 13th 2010 at 12:40 PM.
Follow Math Help Forum on Facebook and Google+
For the first n terms the formula is given by: $\displaystyle S_n = \frac{n}{2}(2a + (n-1)d)$ or $\displaystyle S_n = \frac{n}{2}(a+ l)$ where l is the last term that you are counting in. Post what you get.
View Tag Cloud