1. ## Sequence problem

$
\sum_{k=1}^6(-1)^k4^k
$

How do you do this problem?
$-1^6=1$

$4^6=4096$

4096 != 3276
Thanks.

2. Originally Posted by desiderius1
$
\sum_{k=1}^6(-1)^k4^k
$

How do you do this problem?
$-1^6=1$

$4^6=4096$

4096 != 3276
Thanks.
It is a GP with first term -4, common ratio r = -4 and number of terms 6.
So sum S = a[r^n - 1]/(r-1)
= -4(4096 - 1)/(-4-1)