Question

how many terms of an AP9,17,25 must be taken to give sum of636

Answer 1

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

636=n/2(2*9+(n-1)8)

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

1272=n(10+8n)

1272=10n+8n^2

8n^2+10n-1272=0

4n^2+5n-636=0

n=48/4 or -53/4

n=12(-53/4 rejected)