since there is a common difference, d, you have
(4x-1) - x = (3x+6)-(4x-1)
so x = 2 and
a = 2
d = 5
Now you can find
a12 = a+11d
S12 = 12/2 (a + a12)
The first three terms of an ap are x,4x-1,and3x+6 find the first term,12 term,and the sum of the 12terms
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