Quadratic Function Analyzer

The Quadratic Function Analyzer turns a, b and c into the roots, vertex, axis, intercept and a graph, with every step shown.

How to Analyze a Quadratic Function

Enter a, b and c for y = ax² + bx + c. The analyzer works through the discriminant, roots, vertex and intercept, then graphs the parabola.

1

Use the discriminant to see what kind of roots you have

The discriminant is b² − 4ac. If it is positive there are two real roots, if it is zero there is one repeated root at the vertex, and if it is negative the roots are a complex pair and the parabola never touches the x-axis.

2

Solve for the roots

The quadratic formula gives x = (−b ± √(b² − 4ac)) / 2a. The analyzer shows the substitution and simplification, and marks the real roots on the graph as hollow dots on the x-axis.

3

Find the vertex, axis and intercept

The vertex sits at x = −b/2a, and substituting that x back in gives its y value. The vertical line through it is the axis of symmetry. The parabola opens up when a > 0 and down when a < 0, and it crosses the y-axis at c.

Frequently Asked Questions

How do you find the vertex of a parabola?
Compute x = −b/2a, then put that x into the equation to get y. For y = x² − 4x + 3, x = 4/2 = 2 and y = 4 − 8 + 3 = −1, so the vertex is (2, −1).
What does the discriminant tell you?
It tells you how many real roots there are without solving: positive means two, zero means one, and negative means none (two complex roots instead).
How do you tell whether a parabola opens up or down?
Look at a, the coefficient of x². A positive a gives a U shape with a minimum at the vertex; a negative a gives an upside-down U with a maximum at the vertex.
What is the axis of symmetry?
It is the vertical line x = −b/2a through the vertex. The parabola is a mirror image on either side of it, and when there are two real roots they sit the same distance from it.