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What Is a Quadratic Equation? (Mathematics Lesson)

What Is a Quadratic Equation?

A quadratic equation is an equation that may be expressed as:



where, a is the coefficient of the x2 term, b is the coefficient of the x term and c is a constant.

On a graph, a quadratic equation looks like a curve:



Real Examples of Quadratic Equations

Some real examples of quadratic equations of the standard form are given below:



Some quadratic equations are not obviously in standard form, but can be made so with some manipulation:



Solving Quadratic Equations

Solving a quadratic equation means finding the value of x that make y = 0:



The values of x are the roots of the quadratic equation.

There are 3 main ways of solving quadratic equations:

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Note
WHAT'S IN A NAME?

The word 'quadratic' comes from the word 'quad', meaning "square" - because the x is squared.

DIFFERENT FORMS OF QUADRATIC EQUATIONS

The many different forms of linear equations may be quite confusing. But they all have some things in common:

  • There are 2 variables, y and x.

  • There are constants, like 2 or c.

  • The highest power of x is 2.

    If the highest power of x is 1, (i.e.
    a = 0 in the standard form), it is a linear equation:



    These are quadratic equations, not linear equations.

    Neither will you see powers of 3 (cubic equations) or higher:

Y-INTERCEPT

The y-intercept is found by inserting x = 0 into the quadratic equation. This gives:



THERE ARE 2 ROOTS

Quadratic equations always have two solutions.



Sometimes it seems that there is only one root, but it is repeated.



Even when it seems there are no roots, there are two complex roots.