
Mark M. answered 04/25/20
Tutor
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Mathematics Teacher - NCLB Highly Qualified
a10 = a4 + 6d
-15 = -3 + 6d
-12 = 6d
-2 = d
a4 = a1 + 3d
-3 = a1 - 6
3 = a1
S20 = (20/2)[2(3) + 19(-2)]
Can you continue and answer?