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प्रश्न
Find the value of x if 3 + 6 + 9 + ... + 96 = x.
योग
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उत्तर
a = 3
d = 6 − 3
= 3
an = 96
an = a + (n − 1)d
96 = 3 + (n − 1)3
96 − 3 = (n − 1)3
93 = (n − 1)3
`93/3 = n − 1`
31 + 1 = n
n = 32
`S_n = n/2[2a + (n - 1)d]`
= `32/2[2(3) + (32 - 1)3]`
= 16[6 + 31 × 3]
= 16[6 + 93]
= 16 × 99
= 1,584
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