Question 1084203:  Find p so that p+7, 3p+9, p+3,... form an arithmetic sequence 
 Answer by ikleyn(52903)      (Show Source): 
You can  put this solution on YOUR website! . 
Find p so that p+7, 3p+9, p+3 form an arithmetic sequence
 
 
Notice that I took off ". . . " from the condition, since it MUST be so, according to the common sense. 
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This condition is
  =  ,   or
(p+3) - (3p+9) = (3p+9) - (p+7),   which implies
-2p - 6 = 2p +2,
-8 = 4p,
p = -2.
 
 
Solved.
 
 
 
On arithmetic progressions, see the lessons
 
    - Arithmetic progressions
 
    - The proofs of the formulas for arithmetic progressions 
 
    - Problems on arithmetic progressions  
 
    - Word problems on arithmetic progressions
 
    - Mathematical induction and arithmetic progressions
 
    - One characteristic property of arithmetic progressions
 
    - Solved problems on arithmetic progressions 
 
in this site.
 
 
 
Also,  you have this free of charge online textbook in ALGEBRA-II in this site
 
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.
 
 
The referred lessons are the part of this online textbook under the topic "Arithmetic progressions".
 
 
 
 
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