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# C2 geometric series watch

1. How do you do b ? I don't understand why to work out r. For 12 r as the sequence is 12 , 24,36 . R is not the same between each sequence... Thanks
Attachment 502429502411 for this question surely the fourth bounce would be ar3 but the answer is ar4 (3*0.6^4).. why is it like this though? Thanks
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2. (Original post by coconut64)
How do you do b ? I don't understand why to work out or because the sequence is -10,-20,-28 thanks
the sum is made up of a Geometric Series and also an Arithmetic Series...
3. (Original post by coconut64)
How do you do b ? I don't understand why to work out or because the sequence is -10,-20,-28 thanks
The first few terms may be deceptive - think for like r=10, you get 2^ 10 - 120, and 2^10 is greater than 120. (a bit under 2^7)
4. (Original post by the bear)
the sum is made up of a Geometric Series and also an Arithmetic Series...
I think 12 r is an arithmetic series is it?
5. (Original post by coconut64)
I think 12 r is an arithmetic series is it?
6. (Original post by the bear)
Thanks, I have just updated 2 more questions that I am stuck on, can you help?
7. (Original post by SeanFM)
The first few terms may be deceptive - think for like r=10, you get 2^ 10 - 120, and 2^10 is greater than 120. (a bit under 2^7)
Hi,thanks for helping and I think I have figured it out now thanks. Could you help me with the other question that has been uploaded?
8. (Original post by coconut64)
Hi,thanks for helping and I think I have figured it out now thanks. Could you help me with the other question that has been uploaded?
you need to consider that the heights are multiplied by 0.6 each time.
9. (Original post by the bear)
you need to consider that the heights are multiplied by 0.6 each time.
Yes I have taken that into account but when it says after 4th bounce, I don't know which term it is referring to... I thought it would be ar3? Thanks
10. (Original post by coconut64)
Yes I have taken that into account but when it says after 4th bounce, I don't know which term it is referring to... I thought it would be ar3? Thanks
3>3*.6 = after 1 bounce>3*.6*.6= after 2 bounces>3*.6*.6*.6= after 3 bounces>3*.6*.6*.6*.6 = = after 4 bounces

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