SOLUTION: Given two terms of the arithmetic sequence, a7=12 and a10=-9, find a1 and d.

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Question 958597: Given two terms of the arithmetic sequence, a7=12 and a10=-9, find a1 and d.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a%5Bn%5D=a%5B0%5D%2Bn%2Ad
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a%5B7%5D=a%5B0%5D%2B7d=12
a%5B10%5D=a%5B0%5D%2B10d=-9
Subtracting,
a%5B0%5D%2B10d-a%5B0%5D-7d=-9-12
3d=-21
d=-7
Then use either value for find a%5B0%5D.
a%5B0%5D%2B7%28-7%29=12
a%5B0%5D-49=12
a%5B0%5D=61
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a%5Bn%5D=61-7d