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# C1 maths watch

1. How would you work out something like?

55
∑ (7 + 2r)
r=10
2. (Original post by sweetiemelx)
How would you work out something like?

55
∑ (7 + 2r)
r=10
Write it as and evaluate both separately where both are standard arithmetic sequences.
3. (Original post by Zacken)
Write it as and evaluate both separately where both are standard arithmetic sequences.
Thank you and what if r=2 or 3
4. (Original post by sweetiemelx)
Thank you and what if r=2 or 3
Not sure what you mean, you're summing over the relevant r.
5. What the what!!!
What exam board is this?
6. (Original post by LastMinReviseGuy)
What the what!!!
What exam board is this?
Edexcel
7. Where can i find questions like this?
8. For this question I think it's quicker to let
a = 7 + 2(10),
L = 7+2(55)
and use Sn = (n/2)(a + L) = (46/2)(27 + 117) = 3312.
9. Ah i see, does not seem so hard after looking at for a min or 2.
Thanks XOR for writing down your calculations.
10. Do they give you both arithmetic sequences formulas?
11. (Original post by LastMinReviseGuy)
Do they give you both arithmetic sequences formulas?
Nopes. But it's not hard to remember n/2(first term + last term). Or you can derive one from the other.

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