Mathematics
OpenStudy (anonymous):

What is the sum of a 6-term geometric sequence if the first term is 11, the last term is –11,264 and the common ratio is –4?

OpenStudy (dumbcow):

$\large s_{n} = \frac{a_{1}(r^{n}-1)}{r-1}$

OpenStudy (dumbcow):

n =6 a1 = 11 r = -4

OpenStudy (dumbcow):

does that make sense?

OpenStudy (anonymous):

sn=11(-4-1)/-4-1?

OpenStudy (dumbcow):

yes except the " -4" on top should be raised to the 6th power

OpenStudy (anonymous):

okay so -4^6-1?

OpenStudy (dumbcow):

yep

OpenStudy (dumbcow):

make sure you include the negative sign when raising to power.....-4^6 is different than (-4)^6