Algebra 1 · Quadratic Functions
Axis of Symmetry
Algebra 1 · Quadratic Functions
Definition
The axis of symmetry is the vertical line x = −b/(2a) that divides a parabola into two mirror images.
Examples
- For y = x2 − 2x − 3, the axis is x = 1.
- For y = x2 + 4x, the axis is x = −2.
Key rule
Use x = −b/(2a) to find the line of symmetry.
Memory hook
Axis of symmetry: x = −b over 2a.