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A level OCR Core 2 sequences and series watch

1. _ _ 10 _ _ 80
1) find the common ratio
2) the first term
3) sum of the first six terms

Anyone know how to do this question ??
And if they could kind of show me how to get the answer I would be very grateful xx

Posted from TSR Mobile
2. (Original post by TheDapperNapper)
_ _ 10 _ _ 80
1) find the common ratio
2) the first term
3) sum of the first six terms

Anyone know how to do this question ??
And if they could kind of show me how to get the answer I would be very grateful xx
The question would be nice

I assume this is a geometric sequence

1. How many times do you multiply by r to get from 10 to 80, hence what is r
2. Go back from 10 using r to get a
3. Use the formula
3. (Original post by TheDapperNapper)
_ _ 10 _ _ 80
1) find the common ratio
2) the first term
3) sum of the first six terms

Anyone know how to do this question ??
And if they could kind of show me how to get the answer I would be very grateful xx

Posted from TSR Mobile
I assume this is a geometric series with common ratio r. This means that each term is r multiplied by the previous term:

Can you 'see' what r is by thinking about how to get from 10 to 80?

Then you can go back through the sequence to find the first term and add up all the terms to find the sum.
4. (Original post by TheDapperNapper)
_ _ 10 _ _ 80
1) find the common ratio
2) the first term
3) sum of the first six terms

Anyone know how to do this question ??
And if they could kind of show me how to get the answer I would be very grateful xx

Posted from TSR Mobile
Start by converting the info you have into a form you're comfortable with - e.g. call the first term a and the common ratio r.

Then the second term is ar, the third term etc.
Set up formulas for the 3rd and 6th terms - this will give you the common ratio. Then you can take it forward from there
5. Thank you peeps its helped a lot ! Muchos Gracias

Posted from TSR Mobile
6. Oops Muchas Gracias haha

Posted from TSR Mobile

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