Question

how many terms of AP 9,17,25.... must be taken to give a sum of 636​

Answer 1

Answer:

n=12

Step-by-step explanation:

a =9, d =8 Sn= 636

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

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

1272=10n+8n^2

by simplifying-

4n^2+5n-636=0

4n^2-48n+53n-636=0

4n(n-12)+53(n-12)=0

(4n+53)(n-12)=0

n=12 or n = 53/4..

As we are looking for an integer value-

n=12

Hope You understand !!

Answer 2

Answer:

here,

a=9

d=17-9=8

Sn=636

Sn=n/2[2a+(n-1)d]

632×2=n[18+(n-1)8]

1264=18n+8n²-8n

8n²+10n-1264=0

4n²+5n-632=0