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1.6.15 Standard formulae for geometric series (A-level only)

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Question 20

A geometric sequence has first term aaa and common ratio rrr, where r>0r > 0r>0.

Given that

  • the 2nd term is 12
  • the 4th term is 6.75
a.

Show that r=0.75r = 0.75r=0.75.

[2]
b.

Hence find the value of aaa.

[1]
c.

Given that the sum of the first nnn terms of this sequence is greater than 63.5

Find the smallest possible value of nnn.

(Solutions based entirely on graphical or numerical methods are not acceptable.)

[5]

1.6.15 Standard formulae for geometric series (A-level only) Questions

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