SOLUTION: What is the 21st term of {-5, -11, -17,...}

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Question 1185122: What is the 21st term of {-5, -11, -17,...}
Answer by MathLover1(20850) About Me  (Show Source):
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-5, -11, -17
find differences
-5.......... -11.............-17
.......-6.............-6
The formula for nth term of an arithmetic progression is+a%5Bn%5D=a%5B1%5D%2Bdn-d. In this example we have d=-6 and +a%5B1%5D=-5, so
a%5Bn%5D=-5-6n-%28-6%29
a%5Bn%5D=-5-6n%2B6
a%5Bn%5D=-6n%2B1

then the 21st term is:
->+n=21
a%5B21%5D=-6%2A21%2B1
a%5B21%5D=-125