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# Arithmetic sequence help watch

1. http://i.imgur.com/IFj79bdh.jpg

Question 7, only one driving me nuts. I tried doing it as simultaneous equations but no dice
2. (Original post by WilliamSlim)
http://i.imgur.com/IFj79bdh.jpg

Question 7, only one driving me nuts. I tried doing it as simultaneous equations but no dice
You're using simultaneous equations which suggests to me that you're using a common difference variable d in your working (let me know if I'm wrong).

But you don't need to involve 'd' here. For arithmetic sequences, the differences between pairs of consecutive terms is always the same. E.g. for 3, 5, 7, 9, ..., 3 - 5 = 7 - 5 = 9 - 7 etc.

Can you see how to use that for this question?
3. (Original post by WilliamSlim)
http://i.imgur.com/IFj79bdh.jpg

Question 7, only one driving me nuts. I tried doing it as simultaneous equations but no dice
17x - x2 = x2 - (-8)

edit: too late/I am out
4. (Original post by notnek)
You're using simultaneous equations which suggests to me that you're using a common difference variable d in your working (let me know if I'm wrong).

But you don't need to involve 'd' here. For arithmetic sequences, the differences between pairs of consecutive terms is always the same. E.g. for 3, 5, 7, 9, ..., 3 - 5 = 7 - 5 = 9 - 7 etc.

Can you see how to use that for this question?
So i would just do (-8) - (x^2)=(x^2)-(17x) ?
5. (Original post by WilliamSlim)
So i would just do (-8) - (x^2)=(x^2)-(17x) ?
Yes, that will work. Simplify then solve the quadratic.
6. (Original post by notnek)
Yes, that will work. Simplify then solve the quadratic.
Thanks man, if i ever meet you in real life i'll give you a back massage

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