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प्रश्न
The first term and the common difference of an A. P. is 10,000 and
2000 resectively. Find the sum of first 12 terms of the A.P.
उत्तर
a = 10,000, d = 2000 , S12 = ?
`S_n = n/2[2a+(n-1)d]`
`∴ S_12 = 12/2 [2xx10,000+(12-1)xx 2000]`
`=6(20,000+11 xx 2000)`
`=6(20,000 + 22,000)`
`= 6xx42,000)`
`=2,52,000`
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