SOLUTION: A quadratic function has an axis of symmetry of x=4, a y-intercept of 33 and also passes through the point, P(5,3). Write the equation of this function in the form of y=ax^2+bx+c.

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: A quadratic function has an axis of symmetry of x=4, a y-intercept of 33 and also passes through the point, P(5,3). Write the equation of this function in the form of y=ax^2+bx+c.       Log On


   



Question 355341: A quadratic function has an axis of symmetry of x=4, a y-intercept of 33 and also passes through the point, P(5,3). Write the equation of this function in the form of y=ax^2+bx+c.
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
A quadratic function has an axis of symmetry of x=4, a y-intercept of 33 and also passes through the point, P(5,3). Write the equation of this function in the form of y=ax^2+bx+c.
Let's draw what we have,  Since its y-intercept is 33, it passes
through the point (0,33). We will draw its axis of symmetry and plot
the points (0,33) and (5,3).




Since the line x=4 is the axis of symmetry and since the point
(5,3) is on the graph, its reflection across the line x=4 is
also a point on the graph.  That point is (3,3).  Also the
reflection of the y-intercept (0,33) across the line of symmetry 
is also a point on the graph.  That point is (8,33).  So we have 
four points on the parabola and we only need three.

   


So we pick any three of the four points and substitute them in

y=ax%5E2%2Bbx%2Bc

Substituting in (0,33)

33=a%280%29%5E2%2Bb%280%29%2Bc
33=c

So we already have c=33:

y=ax%5E2%2Bbx%2B33

Substituting (8,33) in that

33=a%288%29%5E2%2Bb%288%29%2B33
33=64a%2B8b%2B33
0=64a%2B8b
0=8a%2Bb

Substituting (3,3) in that

3=a%283%29%5E2%2Bb%283%29%2B33
3=9a%2B3b%2B33
-30=9a%2B3b
-10=3a%2Bb

system%280=8a%2Bb%2C-10=3a%2Bb%29

Solve that system and get a=2 and b=-16

So the parabola's equation is

y=2x%5E2-16x%2B33

and here is its graph: 



Edwin