Write the equation of a parabola having the vertex (1, −2) and containing the point (3, 6) in vertex form. Then, rewrite the equation in standard form. [Hint: Vertex form: y - k = a(x - h)2]

Respuesta :

PART A

The equation of the parabola in vertex form is given by the formula,

[tex]y - k = a {(x - h)}^{2} [/tex]

where

[tex](h,k)=(1,-2)[/tex]

is the vertex of the parabola.

We substitute these values to obtain,


[tex]y + 2 = a {(x - 1)}^{2} [/tex]

The point, (3,6) lies on the parabola.

It must therefore satisfy its equation.


[tex]6 + 2 = a {(3 - 1)}^{2} [/tex]


[tex]8= a {(2)}^{2} [/tex]


[tex]8=4a[/tex]


[tex]a = 2[/tex]
Hence the equation of the parabola in vertex form is


[tex]y + 2 = 2 {(x - 1)}^{2} [/tex]


PART B

To obtain the equation of the parabola in standard form, we expand the vertex form of the equation.

[tex]y + 2 = 2{(x - 1)}^{2} [/tex]

This implies that

[tex]y + 2 = 2(x - 1)(x - 1)[/tex]


We expand to obtain,


[tex]y + 2 = 2( {x}^{2} - 2x + 1)[/tex]


This will give us,


[tex]y + 2 = 2 {x}^{2} - 4x + 2[/tex]


[tex]y = {x}^{2} - 4x[/tex]

This equation is now in the form,

[tex]y = a {x}^{2} + bx + c[/tex]
where

[tex]a=1,b=-4,c=0[/tex]

This is the standard form