Question

Find S5 of the A.P. 8, 6, 4, ... .​

Answer 1

a=8 , l=0 ( last term )

n=5

Sn=n/2(a+l)

Sn=5/2(8)

Sn=20

S5=20

Answer 2

Answer:

a= 8

d= a2 - a1

= 6 - 8 = -2

we have to find sum of 5 term

so, Sn = n/2(2a+(n-1)d)

=5/2(2×8+(5-1) -2

=5/2(16+(-8)

=5/2×8

=20 ans