If sum of an n terms of an AP is 2n^2 + 5n, then find its nth term.
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Sn = 2n^2 + 5n
S1 = 2 ×(1)^2 + 5×1
=2+5
=7.
S1 = a1.
therefore, a1 = 7.
S2 = 2×(2)^2 + 5×2
=8+10
=18.
now, a2= (S2-S1)
=(18-7)
=11.
d=(a2-a1)
=(11-7)
=4.
now,an= a +(n-1)d.
= 7+(n-1)4
=7+4n-4
=3+4n.
hence,nth term is 3+4n.
S1 = 2 ×(1)^2 + 5×1
=2+5
=7.
S1 = a1.
therefore, a1 = 7.
S2 = 2×(2)^2 + 5×2
=8+10
=18.
now, a2= (S2-S1)
=(18-7)
=11.
d=(a2-a1)
=(11-7)
=4.
now,an= a +(n-1)d.
= 7+(n-1)4
=7+4n-4
=3+4n.
hence,nth term is 3+4n.
426ri543:
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