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
