## anonymous 4 years ago 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?

1. anonymous

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

2. anonymous

n =6 a1 = 11 r = -4

3. anonymous

does that make sense?

4. anonymous

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

5. anonymous

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

6. anonymous

okay so -4^6-1?

7. anonymous

yep

8. anonymous

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