how many terms of an AP 9,17,25....... must be taken to give the sum of 6367 ..plz answer
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Here the first term = a = 9
The common difference = d = 8
We have to find the number of terms i.e. 'n'
We have,
Sn= (n/2)[2a+(n-1)d]
636=(n/2)[18+8n-8]
1272=n(8n+10)
Hence we get the quadratic eqn,
8n²+10n-1272=0
i.e. 4n²+5n-636=0
By solving the above quadratic eqn,
We get n=12
Hence the sum of first 12 terms of the given A.P. will be 636.
hope that help you......
The common difference = d = 8
We have to find the number of terms i.e. 'n'
We have,
Sn= (n/2)[2a+(n-1)d]
636=(n/2)[18+8n-8]
1272=n(8n+10)
Hence we get the quadratic eqn,
8n²+10n-1272=0
i.e. 4n²+5n-636=0
By solving the above quadratic eqn,
We get n=12
Hence the sum of first 12 terms of the given A.P. will be 636.
hope that help you......
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