Haju24 Haju24
  • 21-03-2019
  • Mathematics
contestada

How many terms of the AP 9,17,25.... Must be taken to give a sum of 636?​

Respuesta :

Аноним Аноним
  • 21-03-2019

Answer:

A.p= 9,17,25

a=9

d=17-9

=8

Sum of n terms=n÷2[2a+(n-1)d

Step-by-step explanation:

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

mark brainliest   :)

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