y^2=12x

Find each parabola's focus and directrix. Then sketch the parabola. Include the focus and directrix in your sketch.

How do I find focus and directix? This formula sheet gives me a headache.

Focus F ( 3 ; 0 ), directrix D : X = -3

For symmetrical reason, the focus is on the X-axis, while the directrix is parallel to the Y-axis.

Draw a line parallel to the Y-axis and passing through the focus : it meets the parabola at 2 points.
Express the coordinates of any of these 2 points to get the answer : remember that any point of the parabola is at the same distance from the focus than from the directrix.

I don't understand how you got your answer =/

read http://www.protutorcompany.com/finding-the-vertex-focus-and-directrix-of-a-parabola-given-in-standard-form/

the main formula is 1/(4a)
once you find your vertex you can just add (1/(4a)) appropriately
in your case, to the x coordinate of your vertex

remember to get in standard form before you begin using 1/(4a)
ax^2+bx+c=0

This post was edited by saber_x3 on Aug 23 2014 03:35pm

What is the definition of a focus that you've learnt ? And a directrix ?

Where is the Y ?

And before you do a quick fix : it's impossible to get a standard form from Y² = 12X.
Or you would have to exchange X's and Y's.

I'm good to go with this answer.