# Help me? AQA Core 2 maths questionWatch

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Thread starter 3 years ago
#1
Could anyone help me with part C of this question? I've been trying to learn about series today and I'm a bit confused, how can you find the sum of a series that doesn't have an end? I've had a look at the mark scheme and am none the wiser

1
3 years ago
#2
hmmmmmm... Is the answer 25.92?
1
Thread starter 3 years ago
#3
(Original post by kellyalisonchow)
hmmmmmm... Is the answer 25.92?
Yeah it is
0
3 years ago
#4
(Original post by lacee_)
Could anyone help me with part C of this question? I've been trying to learn about series today and I'm a bit confused, how can you find the sum of a series that doesn't have an end? I've had a look at the mark scheme and am none the wiser

1. The sum to infinity of a geometric series that converges can be found using the formula

s = a / (1-r)
Where a is the first term and r is the common ratio.
For part C, you simply minus the first 3 terms of the series from your answer to part B
1
3 years ago
#5
it helps if you understand what the notation used in (c) actually means:

it says "add up all the terms of the sequence from the 4th term up to infinity"

Since you have already found the "sum to infinity" - which means from the first term up to infinity - in part (b), what you need to find now is the sum of all the terms less the first three. You are given the first term (48), and how to generate the next term (x0.6) and you have also found the third term in part (a), so you are ready to go!
1
3 years ago
#6
(Original post by lacee_)
Yeah it is
SO... the question wants you to find the sum to infinty start from the 4th term
which would be this
Sum to infinity- sum of the first 3 terms
= ans(b) minus 94.0
=120-94.08
=25.92
0
Thread starter 3 years ago
#7
Much clearer now, I guess I just didn't really understand the notation properly. Thanks everyone
0
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