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Earlier discussion
1 older comment kept for context.
Oluwaseun Adeyemi
T1, T2, T3
2, -9, -20 .... -141
l = a + (n - 1)d
First term, a = 2
Common difference, d = T3 - T2
= T2 - T1
= -20 - (-9) = -9 -2
= -20 + 9
= -9 - 2
= -20 + 9
= -11
-11 = -11
d = -1
Last term, L = -141
-141 = 2 + (n - 1) (-11)
-141 = 2 + (-11 n + 11)
= 2 - 11n + 11
-141 = 13 - 11n
-141 - 13 = -11n
-154 = -11n
n = \(\frac{-154}{-11}\)
n = 14