Question

find the sum of A. P. 8,3,-2,-7,-12,... up to n terms

Answer 1

its an ap
simply apply formula
s = (n /2)[ 2*first term + (n-1)*common diff ]

Answer 2

Step-by-step explanation:

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

a=8 d=-5

by substituting in formula

sn=n/2[2(8)+(n-1)-5]

n/2[16+(-5n+5)]

n/2[16+5-5n]

n/2[21-5n]

proof :sumof first 3terms(8,3,-2)is9

s3=3/2(21-5(3)

s3=3/2(21-15)

s3=3/2(6)

s3=3*3=9