Question 853096
S = ½(a + an)n
-18 = ½(2a + d(n-1))n
9 = a + (2)d
S = ½(a + an)n
S = ½(2a + d(n-1))n
-18 = a + 3d+ a + 4d
-18 = 2a + 7d
9 = a + 2d
18 = 2a+4d
-18 = 2a + 7d
36=-3d
d=-12
9 = a + 2d
9=a+2*(-12)
9=a-24
33=a
d=-12
33,21,9,-3,-15,-27
a(n) = -3(4n-15)
a(n) = -12n-45

a(n)=33+(n-1)(-12)
a(n+1)n-12
(for all terms given)