# Sum to Infinity of a geometric sequenceWatch

#1
I dont understand where U1+U1r=(48/7) comes from

from what equation does U1+Ur come from?

pls explain, thanks
0
4 years ago
#2
(Original post by sabi06)
I dont understand where U1+U1r=(48/7) comes from
from what equation does U1+Ur come from?
0
#3
(Original post by TeeEm)
yeah i did, can you see it?
im not sure why it does show up at first
0
4 years ago
#4
(Original post by sabi06)
yeah i did, can you see it?
im not sure why it does show up at first
Sinf = a/(1-r) is a standard formula where a = u1 = first term, r = common ratio

7 = a/(1-r)

multiply across and tidy and you get the answer...
0
#5
(Original post by TeeEm)
Sinf = a/(1-r) is a standard formula where a = u1 = first term, r = common ratio

7 = a/(1-r)

multiply across and tidy and you get the answer...
i understood that, but i dont understand U1+U1r = (48/7)

where did U1+U1r come from?
0
4 years ago
#6
(Original post by sabi06)
i understood that, but i dont understand U1+U1r = (48/7)

where did U1+U1r come from?
in a GP terms look like this:

a + ar + ar2 + ar3 + ....

since the first 2 terms add up to 48/7, then a + ar = 48/7.

(this book uses a bit of awkward notation)
0
#7
(Original post by TeeEm)
in a GP terms look like this:

a + ar + ar2 + ar3 + ....

since the first 2 terms add up to 48/7, then a + ar = 48/7.

(this book uses a bit of awkward notation)
thank you again
0
4 years ago
#8
(Original post by sabi06)
thank you again
pleasure
0
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