If the first term of an arithmetic sequence equals the second term minus the third, and the fourth term is 8, what is the first term?
a1 + 3d = 8 8-3d = a1
a1 = a2 - (a2 +d) - a1 = d
8 - (3*-a1) =a1
8 + 3a1=a1
8 = -2a1
a1 = -4 d = 4
-4 0 4 8
+36915 
