Question 1088849: Write the first four terms of an arithmetic sequence whose ninth term is -51 and whose fourth term is -1.
Answer by rothauserc(4718)   (Show Source):
You can put this solution on YOUR website! a(9) = -51 = a(1) + d * (9-1)
1) -51 = a(1) + 8d
:
a(4) = -1 = a(1) + d * (4-1)
2) -1 = a(1) + 3d
:
we have two equations in two unknowns
:
1) a(1) + 8d = -51
2) a(1) + 3d = -1
:
subtract equation 2) from equation 1)
:
5d = -50
d = -10
:
substitute for d in equation 1
:
a(1) + 8(-10) = -51
a(1) -80 = -51
a(1) = 29
:
a(n) = 29 -10 * (n-1)
:
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the first four terms are
29, 19, 9, -1
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