Find a quadratic model for (-1,1), (1,1), (3,9)

Immediate math help from PAID TUTORS. (paid link)Click here to see ALL problems on Quadratic EquationsQuestion 360690: Write a quadratic model for (-1,1) (1,1) (3,9) 
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I can call the points (x1,y1), (x2,y2), and (x3,y3)

Now, plugging in the actual x's and y's

The general form for a quadratic is

Now I can write

(1) 
and

(2) 
and

(3) 
This is 3 equations and 
3 unknowns, so it's solvable
Add (1) and (2) to get

Substitute this in (3)

Now substitute  and  back into (2)
(2) 
(2) 
Now solve for , then do more substitutions to get  and 

The solution is

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