Question

The first term and common difference of an arithmetic sequence is 56 and -8
1) find the 8th term 2)sum of first 15 terms

Answer 1

1)=7

2)=105

Step-by-step explanation:

for 1st answer

a=56

d= -8

an= a+(n-1)*d

a8= 56+(8-1)*(-7)

a8= 56+(7)*(-7)

a8= 56-49

a8=7 .......1st answer

for 2nd answer

S15= n/2*[2a+(n-1)*d]

S15= 15/2*[2<56>+(15-1)*(-7)]

S15= 15/2*[112+(14)*(-7)]

S15= 15/2*[112-98]

S15= 15/2*[14]

S15= 15*7

S15= 105.......2nd answer