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# Help with series and sequences C1 AS Maths please? watch

1. A sequence of numbers a1, a2, a3… is defined by
an+1 = 5an – 3, n>1
given that a2 = 7
find the value of a1

The only thing I can think of is making n = 0
2. Substitute n = 1 into the sequence and see if you can form an equation. The n > 1 is confusing, though, since I am not sure how you could get an answer with anything other than n = 1...
3. (Original post by jessnoch)
A sequence of numbers a1, a2, a3… is defined by
an+1 = 5an – 3, n>1
given that a2 = 7
find the value of a1

The only thing I can think of is making n = 0
You know an+1; rearrange for an. (an will be a1 when an+1 is a2).

I got a1 = 2. Let me know if you need any further help.
4. (Original post by jessnoch)
A sequence of numbers a1, a2, a3… is defined by
an+1 = 5an – 3, n>1
given that a2 = 7
find the value of a1

The only thing I can think of is making n = 0
I would do it this way by re-arranging for an:

If an+1 = 5an - 3 and n>1

Then -4an = -4

so an = 1
5. (Original post by Gareth Owen)
I would do it this way by re-arranging for an:

If an+1 = 5an - 3 and n>1

Then -4an = -4

so an = 1
I think you've misread the question. The equation given by the OP relates successive terms in the sequence, so it should say

for n > 1
6. (Original post by davros)
I think you've misread the question. The equation given by the OP relates successive terms in the sequence, so it should say

for n > 1
Yes you are right so A1 = 2 then. Agreed.

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