Write the equation for a parabola with the vertex at (–1, 3) and the equation of the directrix y = 1. (x – 1)^2 = (y + 3)

(x + 1)^2 = 8(y – 3)

(x – 1)^2 = 8(y + 3)

(y – 3)^2 = 2(x + 1)

answer is (x+1)^2=8(y-3)

How to do this , and can some one explain

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