If nth term of an ap is 2n+1 what is sum of its first three terms
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Given :
nth term = 2 n + 1
= > a₁ = 2 + 1
= 3
= > a₂ = 4 + 1
= 5
d = a₂ - a₁
= > 5 - 3
= 2
Sₙ = n / 2 [ 2 a + ( n - 1 ) d ]
S₃ = 3 / 2 [ 6 + 2 × 2 ]
S₃ = 3 / 2 [ 10 ]
S₃ = 3 × 5
S₃ = 15 .
Therefore , sum of first three numbers is 15 .
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