The sum of first n terms fo an AP is (5n−n2) the nth term of the AP is
(a) (5-2n) (b) (6-2n) (c) (2n-5) (d) (2n-6)
Given that sum of the first n terms of an AP is (5n−n2)
Sn=(5n−n2)
First term, a1=S1=5(1)−(1)2=5−1=4
Sum of first two terms S2=5(2)−(2)2=10−4=6.
Second term, a2=S2−S1=6−4=2
d=a2−a1=2−4=−2
an=a+(n−1)d
=4+(n−1)(−2)
=4−2n+2
=6−2n.
∴ nth term of an A.P = 6 - 2n.
option b is correct