Find the sum of the series...

-2, 1-(1/2)+(1/4)-(1/8)+(1/16)

so i know A1=-2 and r=(-1/2) thanks to @hartnn ....and i was going to use the formula
A1=(1-r^n/1-r) but im not sure what n is:(

Question

Find the sum of the series...

-2, 1-(1/2)+(1/4)-(1/8)+(1/16)

so i know A1=-2 and r=(-1/2) thanks to @hartnn ....and i was going to use the formula 
A1=(1-r^n/1-r) but im not sure what n is:(

megannicole51 · Answer

is there another formula if you dont know what n is?

hartnn · Answer

yes, correct 
r = -1/2
just plug in that formula 
n is just the number of terms, you can count it manually,

megannicole51 · Answer

so n=6?

hartnn · Answer

yup

megannicole51 · Answer

awesome:) that was easy lol

hartnn · Answer

unless there is a ..... in the end

hartnn · Answer

which would make it infinite term series

hartnn · Answer

-2, 1-(1/2)+(1/4)-(1/8)+(1/16) ...... <<<<<infinite series
sum = a/(1-r)

megannicole51 · Answer

i dont see an a so im good with the first formula right? lol

hartnn · Answer

the formula is 
$\huge S_n= a_1\dfrac{1-r^n}{1-r}$

where a1 is the first term

hartnn · Answer

just to confirm .....as i saw A1=... in your question...

megannicole51 · Answer

perfect thats what i used:) i got -21/16

hartnn · Answer

i get that too! :)

megannicole51 · Answer

yay:) i have another question ill repost it:) hopefully it will be as easy as this one!