Question

How many terms of the A.P. 9,17,25,..... must be taken to give a sum of 636 ?

Answer 1

Hallo dear ❤

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A.p= 9,17,25

a=9
d=17-9
=8


Sum of n terms=n/2[2a+(n-1)d

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

636=n/2[18+8n-8]

636=n/2[10+8n]

1272=10n+8n^2

8n^2+10n-1272=0

2[4n^2+5n-636]=0

4n^2+5n-636=0

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

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

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

n-12=0

n=12

12 terms must be given to sum of 636


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Thank you !

Answer 2

HEY mate !! HERE is your answer !!

here in the given question a=9 ,
d= 17-9=8
n=?
sn=636

now putting the formula of sn ,we get.

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

just put the given datas in the appropriate variables then get the value of n.

hope it helps you.

thanks

@pratyush