Question

can someone please help me!
Math each geometric sequence with the correct sum.
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 1,328,600 630/3 765 1441

Answer 1

ok lets do this
since
\[\Large S _{n}=\frac{a _{1}*(1-r^n)}{1-r}\]

Answer 2

so
for case one
a1 = 3, a8 = 384, r = 2
here n=8
\[\Large S _{8}=\frac{3(1-(2)^8)}{1-2}=765\]
for second one
a1 = 80, n= 7, r = - 1/2

\[\Large S _{7}=\frac{80(1-(-1/2)^7}{1+1/2}=\frac{215}{4}\]

can you do the rest by yourself ?

Answer 3

@brendas