Ask a New Question

If the 7th term of AP is 21,find the sum of first 13 terms of AP?

1 answer

a7 = a + d(6) = 21
{so 2a+12 d = 42}

sum of first 13 = (13/2)(2a + 12d)

= (13/2)(42)

= 13 * 21

= 273

look at:
http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html

Ask a New Question or answer this question.

Similar Questions

1) The sum of last three terms of GP having n terms is 1024 time the sume of first 3 terms of GP. If 3rd term is 5. Find the
1. 1 answer
1) In the arithmetic progression, the 8th term is twice the 4th term and the 20th term is 40. Find the common difference and the
1. 4 answers
The third term of a G.P is 24 and the sum of the first two terms is 288. If all the terms are positive,finda)the first term and
1. 1 answer
The 14th term of an arithmetic progression AP is 96 while the 25th term is 173.find theA: 19th terms B:sum of 13th and 53 terms
1. 1 answer

more similar questions