Question

The sum of first n terms of an AP is given by Sn = 2n2

+ 3n . Find the sixteenth term of the AP.

Answer 1

a1 = S1 = 2*1^2 + 3*1 = 5

a2 = S2 - a1 = (2*2^2 + 3*2) - 5 = 9

so d =a2 - a1 = 9-5 = 4

so a16 = a1 + (n-1)d = 5 + (16-1)4 = 65

Answer 2

Hey friend!!


Here's ur answer....


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Sn = 2n² + 3n


S1 = 2 (1)²+ 3(1)
S1 = a = 2 + 3 = 5

S2 = 2(2)² +3 (2)
S2 = 8 + 6
S2 = 14.

We know that :
S2 - S1 = a2
14 - 5 = a2
a2 = 9.

So,a = 5 & a2 =9

So, d = 9 - 5 = 4.

16th term = a +15d
= 5 + 15 (4)
=5 + 60
= 65.



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Hope it may help you....


Thank you :))