Answer:
sn = -216
Step-by-step explanation:
If an arithmetic sequence has a1=5 d=-2 and n=18 what is sn?
The formula for sn is given as:
sn = n/2[2a +(n - 1)d]
Hence, we fill in our values
sn = 18/2 [2 × 5 + (18 - 1)-2]
sn = 9 [ 10 + (17)-2]
sn = 9 [10 - 34]
sn = 9 × -24
sn = -216
