. Using Eucid sdivisag,idtuoCL22idu8. How many terms of the AP: 9, 17,

1.	. Using Eucid sdivisag,idtuoCL22idu8. How many terms of the AP: 9, 17, 25,must be taken to give a sum of 636?
Answer» In given AP we havea=9 d=8 s=636 Let sum of n terms be 636 s(n)=n/2(2a+(n-1)d) 636 x 2 = n (18+8n-8) 1272 = 8n²+10n 636 = 4n²+5n (4n+53) (n-12) ∴ n =12, ignoring fraction So, 12 terms are needed

. Using Eucid sdivisag,idtuoCL22idu8. How many terms of the AP: 9, 17, 25,must be taken to give a sum of 636?

Answer»

In given AP we havea=9

d=8

s=636

Let sum of n terms be 636

s(n)=n/2(2a+(n-1)d)

636 x 2 = n (18+8n-8)

1272 = 8n²+10n

636 = 4n²+5n

(4n+53) (n-12)

∴ n =12, ignoring fraction

So, 12 terms are needed