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Find an equation in the form y equals ax squared plus bx plus cy=ax2+bx+c for the parabola passing through the points. ​(11​,negative 8−8​), ​(negative 5−5​,negative 164−164​), ​(33​,negative 36−36​)

 Nov 5, 2015
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We have this system of equations

 

a(11)^2 + b(11) + c  = -8   →       121a + 11b + c  = -8      (1)

a(-5)^2 + b(-5)  + c  = -164  →      25a  -   5b + c  = -164   (2)

a(33)^2 + b(33) + c = -36   →     1089a + 33b + c  = -36    (3)

 

Multiply (2) by -1  and add to (1)   ......this gives

 

96a + 16b  =  156   (4)

 

Multiply (1) by -1 and add to (3).......this gives

 

968a + 22b = -28   (5)

 

Multiply (4) by -22 and (5) by 16.....this gives

 

-2112a    -352b = -3432   (6)

15488a +352b  = - 448   (7)

 

Add (6) and (7) together

13376a = -3880   (8)

 

Divide both sides of (8)  by 13376  and a = -485/1672

 

And using (4) to solve for b, we have

 

96(-485/1672) + 16b = 156    →  b = 4803/418

 

And using (1) to solve for c, we have

 

121(-485/1672) + 11(4803/418) + c  = -8  →   c =  -15093/152

 

So the equation is ... y = (-485/1672)x^2 + (4803/418)x - 15093/152

 

Here's the graph of the parabola......https://www.desmos.com/calculator/dukrb3wrm2

 

 

cool cool cool

 Nov 5, 2015
edited by CPhill  Nov 5, 2015

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