SOLUTION: Write a rule for the nth term of the arithmetic sequence, then find a23 d=-2/3,a4=18

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Question 753616: Write a rule for the nth term of the arithmetic sequence, then find a23
d=-2/3,a4=18
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad
Since d=-2%2F3 and a%5B4%5D=18,
18=a%5B1%5D%2B%284-1%29%2A%28-2%2F3%29 --> 18=a%5B1%5D%2B3%2A%28-2%2F3%29 --> 18=a%5B1%5D-2 --> 18%2B2=a%5B1%5D --> a%5B1%5D=20
So
a%5B23%5D=a%5B1%5D%2B%2823-1%29%2Ad --> a%5B23%5D=20%2B22%2A%28-2%2F3%29 --> a%5B23%5D=60%2F3-44%2F3%29 --> highlight%28a%5B23%5D=16%2F3%29%29 or highlight%28a%5B23%5D=5%261%2F3%29%29