Q. 384.2( 5 Votes )
If the number of terms of an A.P. be 2n + 3, then find the ratio of sum of the odd terms to the sum of even terms.
Given: Total number of terms = 2n + 3
Let the first term = a
and the common difference = d
Then, ak = a + (k – 1)d …(i)
Let S1 and S2 denote the sum of all odd terms and the sum of all even terms respectively.
S1 = a1 + a3 + a5 … + a2n+3
= (n + 2)(a + nd + d) …(ii)
And, S2 = a2 + a4 + a6 … + a2n+2
= (n+1)(a + nd + d) …(iii)
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The sum of n terms of an A.P. is 3n2+ 5n. Find the A.P. Hence, find its 16th term.KC Sinha - Mathematics