Question

if the sum of n terms of an AP is 3nsquare+5n and Tm =164 ,then m equals to

Answer 1

Sn =3n^2 +5n
s1 =3×1×1+5×1=8
s2 =3×2×2+5×2=22
a=8 , a2 =22-8=14
a=8 ,d=6
a+(m-1)d = 164
8+(m-1)6 =164
m-1×6=156
m-1= 26
m=27