How many terms of the A.P:9, 17, 25, ...
must be taken to give a sum of 636?
with brief
Answers
Answered by
3
Answer:
a=9
d=8
Sn=636
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(square)
8n2+10n-1272
2(4n2-5n-636)=0
4n2-5n-636=0
product:2544
sum:5
4n2+53n-48n-636=0
n(4n+53)-12(4n+53)=0
(n-12)(4n+53)=0
(n-12)=0
n= 12 Ans
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3
Answer:
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