what is the sum of the geometric sequence -3,18,-108.. if there is 7 term?

Question

anonymous · Answer

a=first term=-3 ,r=common ratio=-6 ,n=number of all terms=7 .
Use the Rule :
$$\huge \rightarrow Sn=\frac{a(1-r^n)}{1-r}$$

anonymous · Answer

okay.... now what?

anonymous · Answer

Now substitute instead of each variable its number as i listed to u

anonymous · Answer

so whats the answer?

anonymous · Answer

u can evaluate it :D
Don't u have a calculator ?

anonymous · Answer

no :(

anonymous · Answer

ok, http://www.online-calculator.com/ :D

anonymous · Answer

please, please help. im on my last test in the whole class.

anonymous · Answer

please give me the answer, i dont normally ask for answers but i have about 20 minutes left until i get kicked out of the test and i wont be able to graduate if i dont finish up.

anonymous · Answer

Ok
The final answer is :119973

anonymous · Answer

isnt it a negative?

anonymous · Answer

Sry ,your are right ..
Its -119973

anonymous · Answer

thanks :)

anonymous · Answer

Good Luck with your test.