Question

the sum of first n terms of an A.P. is given by Sn = 2n square+3n. find the sixteenth term of the A.P.

Answer 1

Sn = 2n^2 +3n
S1 = 2(1)^2 + 3(1)
S1=2+3=5
S2=2(2)^2+3(2)=8+6=14
A1=first term =5
second term = A2 =s2-s1=14-5=9
Common difference = a2-a1=9-5=4
A16 = a +15d = 5+ 15(4) = 5+ 60 = 65