Question

I need help with parabola directrix and focus.

Answer 1

Here is the question.

Answer 2

I can move the yellow dot, the focus, and the yellow line, the directrix.

Answer 3

@mathmale @Hero

Answer 4

And i have to move the yellow dot and line so that the equation of the function (on the right) is the same as the question (on the top.)

Answer 5

Still need help?

Answer 6

@venny cmon help me?

Answer 7

go here http://www.twiddla.com/1700052

Answer 8

\(y+0=\frac{1}{4}(x+0)^2\)
Here \(y=\frac{1}{4p}x^2\)
\(p=1\)
The distance between the vertex at \((0,0)\) and the focus is 1, place the focus at \((0,1)\)
And the directrix at \(y=-1\)

Answer 9

But HOW do i answer this question, not what is the answer.

Answer 10

Venny why did u leave?

Answer 11

Step 1: Move the directrix to y = 4
Step 2: Move the focus to (+3/2, -3)
Step 3: Make sure the equation on the right reads: y - 1/2 = -1/14(x - 3/2)^2

You are done!

If you want to know how I did the above steps, watch his previous videos or read online articles that explain how to find the equation for the directrix and find the focus from the equation of a parabola.

Answer 12

@hero HELP

Answer 13

http://www.twiddla.com/1700052

Answer 14

Did you carry out the steps in my previous reply?

Answer 15

I don't understand how to do it, first of all. I know how to find the vertex, but after that I don't know what to do.

Answer 16

You don't know how to move the directrix or focus in that khan academy page?

Answer 17

I can move both, and I know how to.

Answer 18

By moving were you able to get y - 1/2 = -1/14(x - 3/2)^2 on the right hand side to match the given equation?

Answer 19

Can you go to http://www.twiddla.com/1700052 so you can draw what you mean on the graph?

Answer 20

Nothing fancy required here. You just said you know how to move the directrix and the focus in the khan academy page. I am saying moving the directrix so that it passes through the point (0, 4) That is y intercept = 4

Answer 21

After you do that let me know.