Given:
The focus of the parabola is at (6,-4).
Directrix at y=-7.
To find:
The equation of the parabola.
Solution:
The general equation of a parabola is:
[tex]y=\dfrac{1}{4p}(x-h)^2+k[/tex] ...(i)
Where, (h,k) is vertex, (h,k+p) is the focus and y=k-p is the directrix.
The focus of the parabola is at (6,-4).
[tex](h,k+p)=(6,-4)[/tex]
On comparing both sides, we get
[tex]h=6[/tex]
[tex]k+p=-4[/tex] ...(ii)
Directrix at y=-7. So,
[tex]k-p=-7[/tex] ...(iii)
Adding (ii) and (iii), we get
[tex]2k=-11[/tex]
[tex]k=\dfrac{-11}{2}[/tex]
[tex]k=-5.5[/tex]
Putting [tex]k=-5.5[/tex] in (ii), we get
[tex]-5.5+p=-4[/tex]
[tex]p=-4+5.5[/tex]
[tex]p=1.5[/tex]
Putting [tex]h=6, k=-5.5,p=1.5[/tex] in (i), we get
[tex]y=\dfrac{1}{4(1.5)}(x-6)^2+(-5.5)[/tex]
[tex]y=\dfrac{1}{6}(x-6)^2-5.5[/tex]
Therefore, the equation of the parabola is [tex]y=\dfrac{1}{6}(x-6)^2-5.5[/tex].