# New Spec A Level Sequences

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#1
The first three terms of a geometric sequence are:

k+2, 4k, 2k^2, k>0

Find the value of k.

I got k=10 after setting k+2+4k equal to the Sn equation? I worked out r as k/2.

Is this right? Thank you!
0
2 years ago
#2
(Original post by IzzyLJB)
The first three terms of a geometric sequence are:

k+2, 4k, 2k^2, k>0

Find the value of k.

I got k=10 after setting k+2+4k equal to the Sn equation? I worked out r as k/2.

Is this right? Thank you!
Can check it yourself. If then obviously the second term should be but it's not that!

Meaning you did it wrong.

Why not just make the ratios between consecutive terms the same since that must be true on a geo sequence??

I.e. 0
2 years ago
#3
Sorry, just found this thread and I’m having problems with the same question. I’d be fine if I could find the common ratio. How can I find the common ratio for that question?
0
2 years ago
#4
(Original post by Ncodling2017)
Sorry, just found this thread and I’m having problems with the same question. I’d be fine if I could find the common ratio. How can I find the common ratio for that question?
I think RDKGames gives you the ratio for the first and second two terms and makes them equal (which it must be for a geometric progression). Simply solve that equation k and check it works.
0
2 years ago
#5
(Original post by Ncodling2017)
Sorry, just found this thread and I’m having problems with the same question. I’d be fine if I could find the common ratio. How can I find the common ratio for that question?
(Original post by mqb2766)
I think RDKGames gives you the ratio for the first and second two terms and makes them equal (which it must be for a geometric progression). Simply solve that equation k and check it works.
(Original post by IzzyLJB)
The first three terms of a geometric sequence are:

k+2, 4k, 2k^2, k>0

Find the value of k.

I got k=10 after setting k+2+4k equal to the Sn equation? I worked out r as k/2.

Is this right? Thank you!
First term in a geometric series is a (k+2 in this question)
Second term is ar (4k in this question)
Third term is ar^2 (2k^2)

Therefore, using basic power laws, and cancelling stuff

ar/a = ar^2 / ar (cancels to r = r)

so

4k / (k+2) = 2k^2 / 4k

Then you simply solve the equation you have formed to find k.

This is very similar to Question 9 on the 2017 C2 paper (old spec) for Edexcel. Have a go at that. I sat that paper. 2
9 months ago
#6
can anyone solve this
0
1 month ago
#7
k=0 or k=6 I think ?
0
1 month ago
#8
What is the 3 terms geometric sequence of 3, 12, ....
0
1 month ago
#9
0
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