Question

The nth term of an AP is an=2n+1 , find its sum

Answer 1

an = 2n + 1

Therefore,

a1 = 2 × 1 + 1 ______ ( let n = 1 )

a1 = 3_____ ( equation.1 )

Sn = n/2 ( a + an )

( as you did not wrote sum of how many terms I am taking it as 1 )

S1 = 1/2 ( 2 × 3 + 2n + 1 )

S1 = 1/2 ( 6 + 2 × 3 +1 )

S1 = 1/2 ( 13 )

Therefore,

S1 = 13/2

S1 = 7.5

Hope it helps you.

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