Question

In an A.P., the first term is 8, nth term is -33 and the sum to first n terms is 123. Find n and d, the common difference.

Answer 1

Sn=n/2[a+l]
a=8
l=-33
123=n/2[8-33]
246=n[-25]
n=-9.8=10 (check values)
now
l=a+(n-1)d
-33=8+9d
9d=-41
d=-41/9