Answer:
14.5, 13, 11.5
Step-by-step explanation:
The general term (an) of an arithmetic sequence with first term a1 and common difference d is ...
an = a1 + d(n-1)
Then the 8th term is ...
a8 = a1 + d(8-1)
and the 12th term is ...
a12 = a1 + d(12-1)
So, the difference between these terms is ...
a12 -a8 = (a1 +11d) -(a1 +7d) = 4d
= (-2-4) = -6 . . . . . substituting values for a12 and a8
Then the common difference is
... d = -6/4 = -3/2
Using this, we can find a1 from a8.
4 = a1 +7·(-3/2) = a1 - 10.5
14.5 = a1 . . . . . . . add 10.5 to both sides of the equation
This is the first term. The second is this value with the common difference added:
14.5 + (-1.5) = 13
The third term is this with the common difference added:
13 + (-1.5) = 11.5
In summary, the first three terms are ...
14.5, 13, 11.5
