Question

Math each geometric sequence with the correct sum.
a1 = 343, an = -1, r = -1/7
a1 = 3, a8 = 384, r = 2
a1 = 80, n= 7, r = - 1/2
a1 = 5, n= 12, r = 3
a1 = 625, n= 5, r = 3/5
Choose... 215/4 300 1,328,600 630/3 765 1441

Answer 1

helppppppp

Answer 2

u can use
\[ S_n=a_1\cdot\frac{1-r^n}{1-r} \]

Answer 3

what is the r^n

Answer 4

r is the ratio, for instance, in your first example r=-1/7

Answer 5

is that right

Answer 6

in the first you have to find first the number of elements in your sequence

Answer 7

u have a1=343 and r=-1/7 and an=-1

Answer 8

now a2=a1*r
a3=a2*r=a1* r^2 then in general
an=a1*r^(n-1)

Answer 9

-1=343*-1/7^(n-1)

Answer 10

yes