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# Arithmetic Progressions HELP Watch

Q, The first term of an arithmetic series is 3 and the common difference is 2. The sum of the first n terms of the series is 360.
Write down an equation satisfied by n. Hence find the value of n.

2. (Original post by Zeüs)

Q, The first term of an arithmetic series is 3 and the common difference is 2. The sum of the first n terms of the series is 360.
Write down an equation satisfied by n. Hence find the value of n.

You should know that for an arithmetic series, the sum of the first n terms is given by:

If you've not come across this yet, have a look here to see why it works: http://www.mathsisfun.com/algebra/se...rithmetic.html
3. i know this i just don't know how to start
4. (Original post by Zeüs)
i know this i just don't know how to start
The sum is 360. The first term (i.e. a) is 3. The common difference (i.e. d) is 2. Plug all this into the formula above and solve for n.
5. i have 360=n/2(6(n-1)2) i don't know what to do from here
6. (Original post by Zeüs)
i have 360=n/2(6(n-1)2) i don't know what to do from here
Try to set it to n = ...

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