# Quadratic Functions

In this mini-lesson, we will explore the world of quadratic functions in math. You will get to learn about the graphs of quadratic functions, quadratic functions formula, and other interesting facts around the topic. You can also check out the playful calculators to know more about the lesson and try your hand at solving a few interesting practice questions at the end of the page.

The word "**Quadratic**" is derived from the word "**Quad**" which means square.

In other words, a quadratic function is a “ **polynomial** **function of degree 2**.”

There are many scenarios where quadratic functions are used.

Did you know that when a rocket is launched, its path is described by the solution of a quadratic function?

Let's go ahead and learn more about this topic now.

**Lesson Plan**

**What Is a Quadratic Function?**

**Quadratic Function: Definition**

A function of the form \(f(x)=ax^2+bx+c\), where \(a \neq 0\) is called a quadratic function.

Here are some quadratic functions examples.

Functions | Values of \(a\), \(b\) and \(c\) | |
---|---|---|

1. | \(f(x)=8x^2+7x-1\) | \[\begin{align}a&=8 \\b&=7 \\c&=-1 \end{align}\] |

2. | \(f(x)=4x^2-9\) | \[\begin{align}a&=4 \\b&=0 \\c&=-9 \end{align}\] |

3. | \(f(x)=x^2+x\) | \[\begin{align}a&=1 \\b&=1 \\c&=0 \end{align}\] |

4. | \(f(x)=6x-8\) | \[\begin{align}a&=0 \\b&=6 \\c&=-8 \end{align}\] |

Look at Example 4

Here, \(a = 0\). Therefore, it is not a quadratic function.

The remaining functions are quadratic function examples.

**What Is an Example of a Quadratic Function?**

Sometimes, a quadratic function is not written in its standard form, \(f(x)=ax^2+bx+c\), and we may have to change it into the standard form.

Here are some examples of functions and their standard forms.

Functions |
Steps to follow |
Standard Form |

\(f(x)\)=\((x-1)(x+2)\) | Multiply the factors \((x-1)\) and \((x+2)\) | \(f(x)\)=\(x^2+x-2\) |

\(f(x)-x^2\)=\(-3x+1\) | Move the term \(-x^2\) to the right side of the \(=\) sign | \(f(x)\)=\(x^2-3x+1\) |

\(f(x)+5x(x+3)\)=\(12x\) | Expand the bracket on the left side and move \(12x\) to the left side of the \(=\) sign | \(f(x)\)=\(-5x^2-3x\) |

\(f(x)+x^3\)=\(x(x^2+x-3)\) | Expand the bracket on the right side and move \(x^3\) to right side of the \(=\) sign | \(f(x)\)=\(x^2-3x\) |

**Graphs of Quadratic Functions**

This is how the quadratic function is represented on a graph.

This curve is called a **parabola**.

**Quadratic Functions: Calculator**

Now let’s explore some quadratic equations on a graph using the quadratic function calculators.

Drag the values of \(a\) to check for the variations of the upward parabola and downward parabola.

Dragging the values of \(b\) will move the curve either right or left.

Dragging the values of \(c\) will move the curve either up or down.

**Quadratic Functions: Standard Form**

The standard form of a quadratic function is \(f(x)=a(x-h)^{2}+k\), where \((h,k)\) is the vertex of the parabola.** **

This shows the quadratic functions standard form.

If \(a>0\), then the parabola opens upward.

If \(a<0\), then the parabola opens downward.

**Quadratic Functions and Equations**

An equation of the form \(ax^2+bx+c=0\), where \(a \neq 0\) is called a quadratic equation.

So, by a quadratic equation, we mean all the values of \(x\) for which the quadratic function is zero.

**What Is the Quadratic Formula?**

Sometimes working with a hard quadratic function is difficult. But don’t worry! Quadranator is here to help.

Quadranator alone is enough to hunt down all the solutions of the quadratic functions.

The quadratic functions formula is:

This is also called a quadratic formula.

Do you have any difficulty memorizing the quadratic formula?

Don't worry! A rhyme or a song is the best way to remember it.

So, just sing along to the tune of “Pop Goes the Weasel.”

- The standard form of the quadratic function is \(f(x)=ax^2+bx+c\) where \(a\neq0\).
- The curve of the quadratic function is in the form of a parabola.
- The quadratic formula is given by \(\begin{align} \frac{-b \pm \sqrt{b^2-4ac}}{2a}\end{align}\).
- The discriminant is given by \(b^2-4ac\). This is used to determine the nature of the solutions of a quadratic function.
- If \(\alpha\) and \(\beta\) are the two solutions of a quadratic function, then the quadratic equation is given by \(x^2-(\alpha+\beta)x+\alpha\beta=0\).

**Solved Examples **

Example 1 |

Determine the vertex of a quadratic function \(f(x)=2(x+3)^{2}-2\)

**Solution**

Let's express the given quadratic function in the standard function \(f(x)=a(x-h)^{2}+k\).

The function \(f(x)=2(x+3)^{2}-2\) can be written as \(f(x)=2(x-(-3))^{2}+(-2)\)

Here, \(h=-3\) and \(k=-2\)

\(\therefore\) The vertex of the function is (-3, -2) |

Example 2 |

Jack shows a quadratic function.

Can you determine the discriminant?

**Solution**

The quadratic function is \(f(x)=x^{2}+3x-4\)

On comparing it with \(f(x)=ax^2+bx+c\), we get \(a=1\), \(b=3\), and \(c=-4\)

\[\begin{align}\text{Discriminant}&=b^2-4ac\\&=3^{2}-4(1)(-4)\\&=9+16\\&=25\end{align}\]

\(\therefore\), The discriminant is 25 |

Example 3 |

Mia is a fitness enthusiast who goes running every morning.

The park where she jogs is rectangular in shape and measures 12 feet by 8 feet.

A nature restoration group plans to revamp the park and decides to build a pathway surrounding the park.

This would increase the total area to 140 sq. ft.

What will be the width of the pathway?

**Solution**

Let’s denote the width of the pathway as \(x\).

Then, the length and breadth of the outer rectangle is \((12+2x)\;\text{ft.}\) and \((8+2x)\;\text{ft.}\)

The area of the park,

\[\begin{align}(12+2x)(8+2x)&=140\\2(6+x)\cdot 2(4+x)&=140\\(x+6)(x+4)&=35\\x^2+10x-11&=0\end{align}\]

Now we have to find the solution of the quadratic function \(f(x)=x^2+10x-11\)

\[\begin{align}f(x)&=0\\x^2+11x-x-11&=0\\x(x+11)-(x+11)&=0\\(x+11)(x-1)&=0\\x&=1,-11\end{align}\]

Since length can’t be negative, we can only consider \(x=1\)

\(\therefore\), The width of the pathway will be 1 feet. |

- Is it possible to construct a rectangular park with perimeter \(60\;\text{m}\) and area \(200\;\text{sq. m}\). If yes, what will be its length and breadth?
- The sum of two numbers is 45. After subtracting 5 from both numbers, the product of the numbers is 124. What are the numbers?

**Interactive Questions **

**Here are a few activities for you to practice. **

**Select/type your answer and click the "Check Answer" button to see the result.**

**Let's Summarize**

The mini-lesson targeted the fascinating concept of the quadratic function. The math journey around the quadratic function starts with what a student already knows, and goes on to creatively crafting a fresh concept in the young minds. Done in a way that not only it is relatable and easy to grasp, but also will stay with them forever. Here lies the magic with Cuemath.

We hope you enjoyed learning about quadratic functions and equations.

**About Cuemath**

At Cuemath, our team of math experts is dedicated to making learning fun for our favorite readers, the students!

Through an interactive and engaging learning-teaching-learning approach, the teachers explore all angles of a topic.

Be it problems, online classes, doubt sessions, or any other form of relation, it’s the logical thinking and smart learning approach that we, at Cuemath, believe in.

**Frequently Asked Questions (FAQs)**

## 1. What is the general form of a quadratic function?

The general form of a quadratic function is \(f(x)=ax^2+bx+c\), where \(a \neq 0\)

## 2. Find the axis of symmetry with an example.

The axis of symmetry is the vertical line across from the vertex.

Look at the graph of the quadratic function \(f(x)=x^2-6x+5\)

The line \(x=3\) is the line of symmetry.

## 3. How can you find the intercept of the parabola?

\(x\) intercept of a parabola \(f(x)=a(x-h)^{2}+k\) is given by substituting 0 for \(x\) in \(f(x)\).

\(y\) intercept of a parabola \(f(x)=a(x-h)^{2}+k\) is given by solving \(f(x)\) for the variable \(x\).