Question

the sum of first n term of an AP is given by Sn=2n²+3n,find the sixteenth term of the AP

Answer 1

Since
Sn= 2n^2 + 3n
So
S 16 = 2 *(16)^2 + 3*16
= 512 + 48
S 16 = 560

Now,
S 15 = 2*(15)^2 + 3*15
= 450 + 45
S 15 = 495.

Now,
S 16 - S 15 = A 16

since
Sn - Sn-1 = An

therefore
A 16 = 560 - 495
A 16 = 65.

Answer 2

Sn=2n^2 +3n
S16=2(16)^2 +3(16)
=256*2+48
512+48
560
S15=2(15)^2 +3(15)
=225*2+45
=450+45
=495
An=sn-(sn-1)
A16=s16-s15
A16=560-495
=65...ans


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