Answer:
all u have to do is find the second difference
Answer:
The 1st term is -67
Step-by-step explanation:
I. When Sn =
(
)
If Sn = 124, n = 8 and
= 98
124 = 8/2(a + 98)
124 = 4(a + 98)
124 = 4a + 392
124 - 392 = 4a
-268/4 = a
-67 = 
Hope that help :D

Divide both sides by 25 to isolate x: