In the parabola y = a(x − h)^2 + k, what is the axis of symmetry's equation?

• A. y = k
• B. x = h
• C. x = h^2
• D. y = a

Answer: (B)

Symmetry in a parabola written as y = a(x − h)^2 + k is centered on the vertex. The vertex sits at (h, k), and the squared term means the graph mirrors itself across the vertical line that passes through that vertex. So the axis of symmetry is the vertical line x = h. For any offset t, the points (h + t, y) and (h − t, y) have the same y-value, showing the reflection across x = h. The other options don’t describe the line that the parabola reflects about: a horizontal line like y = k runs left-to-right and doesn’t capture the left-right symmetry, x = h^2 isn’t generally a vertical line through the vertex, and y = a is horizontal and unrelated to the reflection axis.