Derive the equation of the parabola with a focus at (2, 4) and a directrix of y = 8. f(x) = −one eighth (x − 2)2 + 6 f(x) = one eighth (x − 2)2 + 6 f(x) = −one eighth (x + 2)2 + 8 f(x) = one eighth (x + 2)2 + 8

A

Step-by-step explanation:

For any point (x, y ) on the parabola the focus and directrix are equidistant

Using the distance formula

= | y - 8 |

Squaring both sides gives

(x - 2)² + (y - 4)² = (y - 8)²

(x - 2)² + y² - 8y + 16 = y² - 16y + 64 ( rearrange and simplify )

(x - 2)² = - 8y + 48

8y = - (x - 2)² + 48

y = - (x - 2)² + 6 → A

step-by-step explanation:

here's what happens:

1) the graph of f   = x^2 is shifted 2 units to the right.

2) the resulting graph is reflected in the x-axis, so that the parabola now opens down.

3) this final result is transformed up by 5 units.