Question

How does one find the focus of a parabola?

Answer 1

do you mean the vertex?

Answer 2

No, like in optics. When you have a parabolic mirror, parallel light rays will focus to one point. How do you find that point given a general formula for the parabola?

Answer 3

I assume u mean the usual ax^2+bx+c form, then the y is obviously the same as the vertex and the x is given by

c - (b^2-1/4a)

Answer 4

Thanks. How did you come up with that?