In An Arithmetic Sequence 13,9,5,1, What Term Is -159?
In an arithmetic sequence 13,9,5,1, what term is -159?
ANSWER :
The term is 44.
STEP BY STEP EXPLANATION :
An = A1 + (n - 1) × R
-159 = 13 + (n - 1) × (9 - 13)
-159 = 13 + (n - 1) × (-4)
-159 = 13 + (-4n) + 4
-159 = (-4n) + 4 + 13
-159 = (-4n) + 17
-4n + 17 = -159
-4n = -159 - 17
-4n = -176
n = (-176)/(-4)
n = 44
- Testing...
An = A1 + (n - 1) × R
A44 = 13 + (44 - 1) × (9 - 13)
A44 = 13 + 43 × (-4)
A44 = 13 + (-172)
A44 = 13 - 172
A44 = -159
Therefore , the term is 44.
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