Question

The sum of the first "n" terms of an AP is n(1+5n).find the first term and the common difference

Answer 1

Step-by-step explanation:

S

n

=5n−n

2

S

1

=a

1

=5(1)−1

2

=4

S

2

=5(2)−2

2

=6

a

2

=S

2

−a

1

=6−4=2

d=a

2

−a

1

=2−4=−2

a

n

=a+(n−1)d

a

n

=4+(n−1)(−2)

∴a

n

=6−2n