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A parabola with equation y = x^2 + bx + c  passes through the points (-1,-11) and (3,17). What is c?

 Feb 2, 2018
 #1
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We have this

 

(-1)^2 + b(-1)  + c  = -11

(3)^2 + b(3)  + c   =  17

 

So we have

 

1 - b  +  c  =  -11

9 + 3b +  c  = 17

 

-b +  c  =  -12       multiply through by -1  =  b - c  = 12     (1)

3b +  c   = 8       (2)

 

Add (1)  and (2)

 

4b  =  20     divide both sides by 

 

b  = 5

 

And using (1)

 

5 - c  = 12    ⇒    c =  -7

 

 

 

cool cool cool

 Feb 2, 2018

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