Question

The sum of n terms of an ap is nsquare+3 find the 20th term of the ap

Answer 1

Sn = n² + 3

S1 = a = 1² + 3 = 4

S2 = 2²+3 = 7

S2 - S1 = a2

⇒ a2 = 7 - 4 = 3

a2 = a+d

⇒ d = -1

→ a20 = a+19d

          = -15

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