SOLUTION: complete the sequence -20;-18;-14;-8 formula for the problem

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Question 948455: complete the sequence -20;-18;-14;-8
formula for the problem
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
-20;-18;-14;-8
Start with -20
-20 +  2 = -18
-18 +  4 = -14
-14 +  6 =  -8
 -8 +  8 =   0
  0 + 10 =  10
 10 + 12 =  22
 22 + 14 =  36
 36 + 16 =  52

To find the general term:

Assume a quadratic general term:

a%5Bn%5D=An%5E2%2BBn%2BC

Substitute 
matrix%281%2C3%2Cn=1%2Cand%2Ca%5B1%5D=-20%29 
matrix%281%2C3%2Cn=2%2Cand%2Ca%5B1%5D=-18%29 
matrix%281%2C3%2Cn=3%2Cand%2Ca%5B1%5D=-14%29 

Solve the resulting system of 3 equations in 3 unknowns
A,B, and C:

The resulting general term when factored is 

a%5Bn%5D=%28n-5%29%28n%2B4%29

Edwin