Help with parabola formula (1 Viewer)

[stormz89]

I know the formula for a parabola is (x - h) = 4a(y - k)
With directix y = -a

But what's the focus and the vertex? I've searched this site for it but its not on here.

Any help would be appreciated.

 

[VenomP]

Vertex you can work out as (h, k) I believe.

If you know the vertex first, then you can figure out focus and directrix easily by moving "a" units along a number plane/graph/whatever they're called.

 

[stormz89]

That means focus is (h, k+a)

Wait, I just remembered theres a square in there

is it x^2 - h or is it (x - h)^2

 

[henry08]

it is (x-h)^2

 

[stormz89]

thankyou, none of my textbooks show that, I remember writing it down but I can't find it.

 

[Mathamagic]

I know the formula for a parabola is (x - h) = 4a(y - k)
With directix y = -a

But what's the focus and the vertex? I've searched this site for it but its not on here.

Any help would be appreciated.

I can help for finding the formula for the focus if eqation of the parabola is stated rightly for exemple . Is the eqation is like (x-h)2 = 4a(y-k) then the formula for focus is (h, k+a) .

 

[lyounamu]

It's not really a set formula. You shouldn't really memorise it but understand it very well.

And the vertex can be changed depending on the question. So just keep that formula in mind and do heaps of questions to see how the question can come in variety of ways.

 

[Trebla]

You should not try to remember the formula. You can easily work out directrix, vertex, focus etc, by simply identifying where 'a' is in the equation and working it out from a diagram. Basically, whichever way the vertex shifts from the origin, is the same amount the focus shifts from the origin. The directrix is simply the y-value 'a' units below the vertex.