Question

in an AP if d= -4, n=7, n2 term=4 find a​

Answer 1

Answer:

We know that S

n

=

2

n

[2a+(n−1)d]

⇒S

n

=

2

n

[a+a+(n−1)d]

⇒399=

2

n

[a+a

n

] [a

n

= last term]

⇒399=

2

n

[1+20]

⇒n=

21

399×2

=38