Axis of Symmetry

The vertical line that splits the parabola down the middle.

The x coordinate of the vertex will always be the Axis of Symmetry because it is where a vertical line can be formed to split a parablo into 2 equal parts.

Therefore the axis of symmetry can be found out in a parabola in vertex form by taking the x coordinate:

Vertex form equation: y = a (x+h)²+k

Vertex: (-h,k)

Axis of Symmetry x=-h

NOTE: Since the Axis of Symmetry is a vertical line, it has to be written:

x=____

Example

Equations of parabola:

y = (x+2)² + 2

What is the Axis of Symmetry?

Solution

Vertex Form Equation: y = (x+2)² + 2

Vertex: (-2, 2)

Axis of Symmetry: x = -2