Axis of symmetry of parabola x² = 4ay (a > 0):
ALine y = x
Bx-axis
CNo axis
Dy-axis (parabola opens up; vertex at origin)
Answer & Solution
Correct answer: D. y-axis (parabola opens up; vertex at origin)
For x² = 4ay: opens up (y > 0), axis is y-axis. Focus (0, a), directrix y = -a, vertex (0,0). Reverse: x² = -4ay opens down.
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