What is the sum of the first 12 terms of the AP -3, 3, 9, 15, 21...?
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Step-by-step explanation:
a = -3
t2 = 3
d = t2 -t1 = 3-(-3) = 6
Sn = n/2 [2a +(n-1)d]
S12 = 6 [ -6 + 33]
= 6[27]
= 162
so sum of first 12 terms is 162
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