Question

If an ap the sum of nth term in n2 plus 2n .Find the 18 thr term

Answer 1

Answer:

S1 = a1 = 1²+2×1 = 3

S2 = a1 + a2 = 2²+2×2 = 8

=> a2 = 8-3 = 5

d = a2 - a1

= 5 - 3 = 2

So, a18 = a + (18-1)d

= 3 + 17 × 2

= 3 + 34 = 37

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