SOLUTION: Find p so that p+7,3p+9,p+3,form an arithmetic sequence

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Question 982791: Find p so that p+7,3p+9,p+3,form an arithmetic sequence
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
d, common difference
system%28p%2B3-%283p%2B9%29=d%2C3p%2B9-%28p%2B7%29=d%29

system%28-2p-6=d%2C2p%2B2=d%29

-2p-6=2p%2B2
-4p=2%2B6
-4p=8
highlight%28highlight%28highlight_green%28p=-2%29%29%29

EITHER equation of the system for evaluating d:
d=2p%2B2
d=2%28-2%29%2B2
d=-2