the sum of first n terms of ap is, 5n^2+3 if its nth term is 168 find n also find the 20th term
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an=168
Sn=5n^2+3
s1 =first term =a
S1=5(1)+3=8
s2=a1+a2
a1=8
S2=5(4)+3=23
=8+a2
a2=15
d=7
a20=a+19d
=8+19X7
=8+133
=141
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wrong
i know the question is wrong not my answer. the sum of first n terms should be 5n^2+3n
but here it is mentioned as 5n^2+3
question inn not correct
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