Question
Fri November 11, 2011 By:

The pth term of an AP is 1 by 7(2p-1). Find the sum of its first n terms.

Expert Reply
Fri November 11, 2011
pth term of an AP = 1 / 7(2p-1).
 
Now let us say p=n, since the above should be true for every value of p.
 
Hence nth term = 1/7(2n-1)
 
And for p=1,  1stterm = 1/7(2×1 - 1) = 1/7
 
We have the formula for sum of n terms as following
 
Sn = n(T1 + Tn)/2   where T1 = first term    and Tn = last term
 
Therfore put the values of first term and nth term from above we get
 
Sn = n[(1/7)+(1/7(2n-1))]/2 
 
   = n [1+ 1/(2n-1)]/14
 
   = n (2n -1 + 1)/ 14(2n - 1)
 
Sn   = n2/7(2n-1)
 
This is answer
 
Thank you
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