Question

How to find a1 if r=-4, an=3072 and Sum of ak=2457 k=1 n

Answer 1

do you know the formula for the sum of a geometric sequence?

Answer 2

Yes, I more need help finding n

Answer 3

\[\sum_{k=1}^{n} a _{k}=2457\]

Answer 4

how do I find n?

Answer 5

the formula, if you may have forgotten is:\[\sum_{1}^{n}a_k=a_1\frac{1-r^n}{1-r}\]
yeah, finding n may be tricky

Answer 6

we might have to define n in terms of a1 ... maybe

Answer 7

a1 is the goal to find

Answer 8

a1 + a1*r + a1*r^2 + .... + a1 r^(n-1) ; since we started with r^0

a1 r^(n-1) = an

Answer 9

we have 2 equations and 2 unknowns

Answer 10

r and \[a_{n}\] are kown

Answer 11

\[a_1r^{n-1}=3072\]
\[a_1\frac{1-r^n}{1-r}=2457\]
got a new keyboard and the put the \ key in the wrong spot .... or at least a different spot and its really annoying me lol