How to Find the Zeros of a Quadratic Function – A Simple Guide

How to Find the Zeros of a Quadratic Function A Simple Guide

To find the zeros of a quadratic function, I first set the function, generally defined as $f(x) = ax^2 + bx + c$, equal to zero.

This equation is pivotal because the zeros are the values of $x$ for which the function $f(x)$ produces a result of zero. They are essentially the points where the graph of the quadratic function intersects the x-axis.

Next, I identify the coefficients $a$, $b$, and $c$ from the quadratic expression.

These values are instrumental when applying various methods to solve for the zeros, such as using the quadratic formula $\frac{-b \pm \sqrt{b^2 – 4ac}}{2a}$, factoring, or completing the square.

Understanding the process behind this mathematical concept is quite valuable in fields such as engineering and physics, where quadratic relationships frequently occur.

The thrill of cracking the code to find the zeros reveals not only the solution to the equation but also a deeper insight into the behavior of parabolic movements in nature. 

Steps Involved in Finding Zeros of a Quadratic Function

When dealing with quadratic functions, I always remember that the zeros are the points where the graph intersects the x-axis.

These points correspond to the values of ( x ) for which the quadratic equation $ax^2 + bx + c = 0$ yields ( y = 0 ). The following steps guide me through finding these valuable zeros.

Step 1: Write the quadratic function in its standard form
The first thing I do is to ensure the quadratic equation is in its standard form, $f(x) = ax^2 + bx + c$, where ( a ), ( b ), and ( c ) are coefficients, and $ a \neq 0$.

Step 2: Factor when possible
If the quadratic function can be factored into the form ( (x – p)(x – q) = 0 ), then finding zeros becomes straightforward. The solutions to ( x ) are the values ( p ) and ( q ), which give the products of zeros equaling ( c ) and the sum of zeros equaling ( -b ).

Step 3: Apply the quadratic formula if factoring is not feasible
Sometimes factoring may not be feasible or apparent, so I then use the quadratic formula: $x = \frac{-b \pm \sqrt{b^2 – 4ac}}{2a}$ This formula calculates the zeros by using the coefficients ( a ), ( b ), and ( c ).

Step 4: Complete the square for a perfect square trinomial
Alternatively, if the quadratic is a perfect square trinomial, I complete the square to find the vertex form $(x – h)^2 = k$, where (h,k) is the vertex. Here, the axis of symmetry is ( x = h ), helping me identify potentially one real zero if ( k = 0 ) or none if $k \neq 0$.

Throughout the process, I closely monitor the discriminant, $b^2 – 4ac$, within the quadratic formula. It tells me how many real zeros to expect:

  • If the discriminant is positive, there are two distinct real zeros.
  • If it is zero, there is one real zero (the vertex lies on the x-axis).
  • If the discriminant is negative, there are no real zeros, only imaginary numbers.

I never forget to consider the domain and range of the function, which for quabdratics, is all real numbers for the domain and depending on the direction of the parabola for the range.

The y-intercept is simply the value of ( f(x) ) when ( x = 0 ), another helpful point on the graph.

Understanding Graphical Methods of Finding Zeros of a Quadratic Function

When I approach a quadratic function, I aim to pinpoint its zeros—the points where the graph intersects the x-axis. These are valuable because they function as solutions to the equation (f(x) = 0).

To begin, I identify the polynomial in standard form, which is $ax^2 + bx + c$. My attention usually goes to the shape of the graph first—a parabola.

If the leading coefficient (a) is positive, the graph opens upwards, and if (a) is negative, the graph opens downwards. This indicates the direction towards the maximum or minimum value of the function, which is at the vertex.

I plot the vertex form $y = a(x-h)^2 + k $, where ( (h, k) ) are the coordinates of the vertex. Whether it’s the maximum or minimum value depends on the sign of (a).

Then, I look for the x-intercepts, which are the zeros, and also the solutions to the quadratic equation. These x-intercepts appear at points where the parabola crosses the x-axis.

Finding these intercepts graphically involves drawing the graph and looking for where ( y = 0 ). The coordinates of these points will be of the form ( (x, 0) ).

If the quadratic has a middle term, it impacts the distance between the x-intercepts and the vertex. To demonstrate, below is a table representing potential x-intercepts for a parabola with their corresponding y-values:

Ordered pairs (x,y)Description
(x_1, 0)First x-intercept
(x_2, 0)Second x-intercept

By plotting these ordered pairs along with the vertex and connecting the points with a smooth curve, I can see the graph of the quadratic function and identify the zeros.

My understanding of the graphical methods not only helps me find these critical points but also to appreciate the symmetry and properties of quadratic functions.

Real-Life Applications of Quadratic Functions

Quadratic functions, which are polynomial functions of degree 2, often appear in various real-life scenarios. One of the most common applications is in analyzing the path of a projectile.

When I launch a rocket or kick a football, for example, the path it takes through the air is parabolic. This parabola can be represented by a quadratic equation of the form $y = ax^2 + bx + c$.

Here, the zeroes of the function represent the points where the projectile touches the ground, assuming level terrain.

Motion Problems: When studying the motion of objects under uniform acceleration, such as gravity, the time ($t$) and height ($h$) can be described by a quadratic equation: $h(t) = -16t^2 + v_0t + h_0$.

The zeroes of this function indicate the time at which the object will return to ground level.

Architecture: Bridge designs often incorporate parabolic arches. The stability of the structure can be analyzed using quadratic functions, where the zeroes help determine if there is a horizontal span that meets the ground or another part of the structure.

Economics: In revenue and profit models, quadratic equations help identify maximum profit points. For a profit function $P(x) = ax^2 + bx + c$, where $x$ is the number of items sold, the zeroes can tell me the break-even points.

Table of Zeroes’ Significance:

Zero of Polynomial FunctionSignificance
Single ZeroIndicates where the function crosses the x-axis
Zero with Multiplicity > 1Implies tangency to the x-axis
Complex ZerosNo real intersection with x-axis

Quadratic functions also help solve everyday problems, like calculating areas or optimizing dimensions for maximum efficiency.

For example, I might use a quadratic function to maximize the fenced area for a given length of fencing by modeling the problem as a rectangle with a fixed perimeter, which leads to a quadratic equation. These are but a few instances where understanding the zeroes and the shape of a quadratic function enrich my grasp of real-world problems.

Examples and Practice Problems

When I tackle the challenge of finding zeros of a quadratic function, I often approach it by seeking the values of ( x ) that make the function equal to zero.

The general form of a quadratic function is $f(x) = ax^2 + bx + c $, where ( a ), ( b ), and ( c ) are constants. Let’s go through a couple of examples together.

Example 1:

For the quadratic function $f(x) = x^2 – 4x + 3$, the roots or zeros can be found by factoring.

f(x) = (x – 1)(x – 3)

Setting each factor to zero gives us the roots:

( x – 1 = 0 ) (Root $x_1 = 1 $)

( x – 3 = 0 ) (Root $ x_2 = 3 $)

Example 2:

Consider $f(x) = 2x^2 – 8x + 6 $, we can still find the roots by factoring, although it might require factoring out a common term first.

$f(x) = 2(x^2 – 4x + 3) = 2(x – 1)(x – 3)$ 

Thus, the roots are again ( x_1 = 1 ) and ( x_2 = 3 ).

To give you some practice, I’ll list a few problems below. Try to factor the quadratic functions to find their zeros.

  1. $f(x) = x^2 – 5x + 6$
  2. $f(x) = 3x^2 – 12x + 9 $
  3. $f(x) = x^2 – 2x – 3 $
ProblemQuadratic FunctionFactored FormRoots
1$ x^2 – 5x + 6$(x – 2)(x – 3) ( x_1 = 2 ), ( x_2 = 3 )
2$3x^2 – 12x + 9 $ 3(x – 1)(x – 3) ( x_1 = 1 ), ( x_2 = 3 )
3$$x^2 – 2x – 3$(x – 3)(x + 1) ( x_1 = 3 ), ( x_2 = -1 )

After you’ve tried these, check your answers against the table to see if you’re getting the hang of it. Working through problems like these is one of the best ways to understand finding zeros in quadratic functions.

Keep practicing, and you’ll see patterns and techniques that make the process even smoother!


I’ve explored various methods to identify the zeros of a quadratic function, each with its unique approach. When working through these techniques, remember that each one applies to different scenarios and offers a distinct perspective on the problem.

Firstly, I can apply factorization to quadratic functions that can be split into binomial products. For example, if I have a quadratic like $f(x) = x^2 – 5x + 6$, I can factor it into $(x – 2)(x – 3) = 0$, finding the zeros at $x = 2$ and $x = 3$.

However, not all quadratics are factored easily which is when I might use the quadratic formula, $x = \frac{-b \pm \sqrt{b^2 – 4ac}}{2a}$. This formula provides a straightforward solution for any quadratic equation.

If I prefer a visual interpretation, graphing the function to find where it intersects the x-axis gives me the zeros as well. This method is particularly intuitive as it reveals how the function behaves overall.

Additionally, completing the square is a more algebraic approach that reshapes the quadratic into a perfect square form, making it easier to solve for $x$. It’s a bit more complex but certainly a valuable tool in my mathematical toolbox.

Each route offers insight into not just the ‘what’ but the ‘why’ of quadratic zeros. My mathematical journey in finding the zeros of a quadratic function is a perfect blend of strategy, logic, and creativity.

I encourage you to practice these methods to gain confidence in solving quadratic equations with ease.