SOLUTION: find N of the arithmetic sequence a1=-6, aN=-23, d=-1

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Question 332879: find N of the arithmetic sequence a1=-6, aN=-23, d=-1
Answer by jrfrunner(365) About Me  (Show Source):
You can put this solution on YOUR website!
in an arithmetic sequence,
the nth term is defined as : a%5Bn%5D=a1%2B%28n-1%29%2Ad
therefore
given: a%5B1%5D=-6, a%5Bn%5D=+-23 and d = -1, substitute into a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad and solve for n
-23=-6+(n-1)*(-1)
-23+6=-(n-1)
17=n-1
18=n
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so, a%5B18%5D=-23 is the 18th term.