Question

If for an A.P the first term is 7 and the common difference is (-2) then find Sn and hence find S8

Answer 1

Step-by-step explanation:

here's your answer....

Answer 2

a=7

d= -2

sn=?

sn= n/2 ( 2a +(n-1)d)

sn= n/2 ( 2(7)+(n-1)(-2))

sn= n/2 (14 -2n+2)

sn= n/2 (16-2n)

sn= n/2 [2(8-n)]

sn= n(8-n)

sn= -n^2 +8n

S8= 8/2 [2(7)+(8-1)(-2)]

S8= 4 [14+(7)(-2)]

S8= 4 [14-14]

S8= 4(0)

S8=0