It seems tough. I did not do it yet, do maybe this would help you. This is not your ordinary parabola i.e. sidewise or normal shaped. This one is a slanted parabola.Originally Posted byc_323_h

Since the vertex is at and focus then, drawing a line between them and extending it in the opposite direction the same distance you end up at . That means the directrix passes through this point. Furthermore, it is perpendicular to the line you drawn. Thus, its slope is using slope and intercept-formula we have,

Thus,

is equation of directrix.

Next, let be any point on the parabola. Then, you know that, the distance to the focus need to be equation to the distance from the line. Thus,

Do not worry the abosolute value disappers when you square both sides.

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I used the formula given a non-vertical line,

and a point not on the line, then the distance is,

Hope this helps.