Question

A parabola can be drawn given a focus of (2, 4)(2,4) and a directrix of x=4x=4. Write the equation of the parabola in any form.

Answer 1

Answer:

The equation of the parabola is;

x = -(1/4)·(y - 4)² + 3

Step-by-step explanation:

The given focus of the parabola is f = (2, 4)

The directrix of the parabola is x = 4

The vertex form of the equation of the parabola can be expressed as follows;

x = a·(y - k)² + h

(y - k)² = 4·p·(x - h)

Where;

(h, k) = The vertex of the parabola

(h + p, k) = The focus of the parabola

x = h - p = The directrix

Therefore, k = 4

h + p = 2...(1)

h - p = 4...(2)

∴ 2·h = 6

h = 6/2 = 3

From equation (1), we have;

p = 2 - 3 = -1

p = -1

From the equation of the parabola in the form, (y - k)² = 4·p·(x - h), we have;

The equation of the parabola is (y - 4)² = 4 × (-1) ·(x - 3)

Therefore, we have;

(y - 4)² = -4·x + 12

4·x = 12 - (y - 4)²

The equation of the parabola is x = -(1/4)·(y - 4)² + 3

y² -8·y + 16 = -4·x + 12

4·x = 8·y - y² - 16 + 12 = 8·y - y² - 4

x = 2·y - y²/4 - 1 = -y²/4 + 2·y - 1

The equation of the parabola can also be written in the form

x = -y²/4 + 2·y - 1 = -0.25·y² + 2·y - 1