What is the equation of the directrix of the parabola y^2 = 8x?
Answer and explanation
Correct answer: A. x = -2
- Step 1: Standard form y^2 = 4ax gives 4a = 8 => a = 2. Step 2. The directrix of y^2 = 4ax is vertical line x = -a = -2. Answer: x = -2. Why not the others: x = 2 passes through the focus of the parabola; y = -2 is a horizontal directrix for an upward parabola; x = -8 substitutes -4a.
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