Question

Find number of terms if sum of A.P-9,17,25,.............
is 636​

Answer 1

Answer:

n=12

Step-by-step explanation:

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

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

1272=n(10+8n)

1272=10n+8n^2

8n^2+10n-1272=0

Divide by 2,

4n^2+5n-636=0

(4n+53)(n-12)

4n+53=0

4n=-53 is not possible

n=12 is possible