Question

How many terms of an A.P. 17,25,…. must be taken to give the sum of 636?

please answer asap!!!! please

Answer 1

Answer:

Explanation:

First term of A.P. = 9 , common difference = 8

 

if sum of n terms 636,  Sn = (n/2) [ 2×9 + (n-1)8 ] = 636

 

Sn = n [ 10+ 8n] = 1272

 

8n2 +10n -1272 = 0  

 

4n2 +5n -636 = 0

 

By factorising LHS, (4n+53)(n-12) = 0

 

hence n = 12