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October 21, 2014

October 21, 2014

Posted by **Remy** on Sunday, September 20, 2009 at 11:17am.

1/2n(n+1)

Find the value of n for which the sum is 105..

Can you show me a step by step please?

- Maths -
**Reiny**, Sunday, September 20, 2009 at 11:32amset 1/2n(n+1) = 105

multiply by 2

n(n+1) = 210

n^2 + n - 210 = 0

(n+15)(n-14) = 0

n = -15 or 14, but n has to be a positive integer, so

there are 14 terms

- Maths -
**Remy**, Sunday, September 20, 2009 at 11:33amThankyou

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