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C2 Maths Question

Hi, I need help answering all of the question below. It is from OCR maths core 2 may 2010.

The question is:

A geometric progression has first term a and common ratio r, and the terms are all different. The first, second and fourth terms of the geometric progression form the first three terms of an arithmetic progression.
(i) Show that r^3 −2r+1=0. [3]
(ii) Given that the geometric progression converges, find the exact value of r. [5]
(iii) Given also that the sum to infinity of this geometric progression is 3 + (square root) 5, find t (4

I'v done part a)

for part b do i sub in values? im so confused
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SH0405
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Original post by notevensoph
Hi, I need help answering all of the question below. It is from OCR maths core 2 may 2010.

The question is:

A geometric progression has first term a and common ratio r, and the terms are all different. The first, second and fourth terms of the geometric progression form the first three terms of an arithmetic progression.
(i) Show that r^3 −2r+1=0. [3]
(ii) Given that the geometric progression converges, find the exact value of r. [5]
(iii) Given also that the sum to infinity of this geometric progression is 3 + (square root) 5, find t (4

I'v done part a)

for part b do i sub in values? im so confused


Solve the quadratic you just found. That should help.

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