Sequences and Series
10
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A geometric series is a+ar+ar2+…a + ar + ar^2 + \dotsa+ar+ar2+…

a.

Prove that the sum of the first n n\,n terms of this series is given by

Sn=a(1−rn)1−r. S_n = \frac{a(1 - r^n)}{1 - r}. Sn​=1−ra(1−rn)​.
[4]
b.

Find

∑k=110100(2k). \sum_{k=1}^{10} 100(2^k). k=1∑10​100(2k).
[3]
c.

Find the sum to infinity of the geometric series

56+518+554+… \frac{5}{6} + \frac{5}{18} + \frac{5}{54} + \dots 65​+185​+545​+…
[3]
d.

State the condition for an infinite geometric series with common ratio r r\,r to be convergent.

[1]

Sequences and Series Questions

Practise Edexcel A Level Old Maths Sequences and Series with exam-style questions for A Level Old Maths. 10 questions, matched to the Edexcel A Level Old Maths (9371) specification and written in Unit exams C1, C2, C3 and C4 plus two applied units (e.g. S1 and M1) style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.

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