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# Arithmatic series watch

1. Hello,

The sum of 1st and 2nd arithamatic series is x. the sum of (n-1th and nth term is Y. Prove n/4(x+y).

thank you.

charikaar
2. (Original post by charikaar)
Hello,

The sum of 1st and 2nd arithamatic series is x. the sum of (n-1th and nth term is Y. Prove n/4(x+y).

thank you.

charikaar

a + (a+d) = x, so 2a+d = x, so 2a = x-d

a+(n-2)d + a+(n-1)d = y, so (n-1)d = y - 2a - (n-2)d

Substitute these in to Sum = n(2a + (n-1)d)/2
3. (Original post by charikaar)
Hello,

The sum of 1st and 2nd arithamatic series is x. the sum of (n-1th and nth term is Y. Prove n/4(x+y).
What**do*you want to prove?

n/4(x+y) what do you want this to equal ?

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Updated: November 18, 2005
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