# Parabola – Formula, Definition With Examples

Updated on January 15, 2024

Welcome to the wonderful world of parabolas, brought to you by Brighterly, your trusted companion in making math learning engaging and fun! Whether you’re an aspiring mathematician or a curious learner, we are here to make complex concepts like parabolas easy to understand.

A parabola, at first glance, may appear to be a simple U-shaped curve. However, as we take a closer look, this curve unveils a mathematical universe filled with captivating secrets and wide-ranging applications. From the natural trajectory of a kicked soccer ball to the perfect shape of a satellite dish, parabolas are all around us. Our journey will take you from understanding the basic definition of a parabola, through its key properties like vertex, focus, and directrix, to writing equations and solving real-life problems using parabolas.

## What is a Parabola?

A parabola is one of the most intriguing yet essential shapes in mathematics. To the uninitiated, it might appear as a simple U-shaped curve. However, delve a bit deeper, and you’ll discover its profound significance in a variety of fields, from mathematics and physics to engineering and even nature itself. As a part of conic sections, parabolas are formed by the intersection of a cone and a plane parallel to one of the cone’s sides. Parabolas can also be considered as the set of all points that are equidistant from a fixed point (the focus) and a fixed line (the directrix).

## Definition of a Parabola

In mathematical terms, a parabola can be defined as the locus of all points in a plane that are equidistant from a given fixed point (the focus) and a fixed line (the directrix). To put it simply, if you draw a line from the focus to any point on the parabola and measure its length, it will be the same as the perpendicular distance from that point to the directrix.

## Derivation of the Formula of a Parabola

The formula of a parabola is derived from its definition. Given a parabola with focus at point F(h, k) and directrix y = k – p (for a vertical parabola), every point P(x, y) on the parabola satisfies the condition PF = PD. By applying the distance formula, we can derive the standard equation of a parabola which is (x-h)² = 4p(y-k) for a vertical parabola, and (y-k)² = 4p(x-h) for a horizontal parabola.

## Features and Properties of a Parabola

A parabola possesses several unique features and properties. The vertex is the ‘lowest’ point of a parabola if it opens upward, or the ‘highest’ point if it opens downward. The axis of symmetry is a line that bisects the parabola into two symmetrical halves. The focus of a parabola is a fixed point inside the curve from which all points on the parabola are equidistant to the directrix, a fixed line outside the parabola.

## Vertex of a Parabola

The vertex of a parabola is the point at which the parabola changes direction. For a vertical parabola, the vertex is the lowest (if it opens up) or highest (if it opens down) point. It’s located at (h, k) in the standard equation of a parabola. The vertex form of a parabola’s equation can be written as y = a(x-h)² + k, where (h,k) is the vertex.

## Axis of Symmetry of a Parabola

The axis of symmetry of a parabola is the vertical or horizontal line that runs through the vertex and divides the parabola into two mirror images. For a vertical parabola in the form (x-h)² = 4p(y-k), the axis of symmetry is x = h. For a horizontal parabola in the form (y-k)² = 4p(x-h), the axis of symmetry is y = k.

## Focus and Directrix of a Parabola

The focus of a parabola is a fixed point located inside the curve, while the directrix is a fixed line that lies outside the curve. For any point on the parabola, the distance to the focus equals the distance to the directrix. For a vertical parabola given by (x-h)² = 4p(y-k), the focus is at (h, k+p) and the directrix is y = k – p.

## Standard Forms of a Parabola

The standard form of a parabola equation can be either for a vertical or a horizontal parabola. The standard form for a vertical parabola is (x-h)² = 4p(y-k), and for a horizontal parabola, it’s (y-k)² = 4p(x-h). Here, (h, k) represents the vertex, and ‘p’ denotes the distance from the vertex to the focus or from the vertex to the directrix.

## Vertical Parabolas

A vertical parabola is one that opens upward or downward. The standard form of a vertical parabola’s equation is (x-h)² = 4p(y-k). When p > 0, the parabola opens upwards and when p < 0, the parabola opens downwards. The vertex is the minimum point for a parabola that opens upwards and the maximum point for one that opens downwards.

## Horizontal Parabolas

A horizontal parabola, on the other hand, opens either to the right or left. Its standard form is (y-k)² = 4p(x-h). If p > 0, the parabola opens to the right, and if p < 0, it opens to the left. For horizontal parabolas, the vertex represents the most extreme left or right point.

## Difference between Vertical and Horizontal Parabolas

The primary difference between vertical and horizontal parabolas is their orientation. Vertical parabolas open upwards or downwards, while horizontal parabolas open to the left or right. Their equations also differ in structure, reflecting the altered relationship between x and y coordinates in each case.

## Equations of a Parabola

The equation of a parabola can be derived in several ways and can take multiple forms. These include the standard form, vertex form, and factored form, each providing different insights into the parabola’s properties. Each form of the equation can be useful depending on the available information and the context in which the equation is used.

## Deriving Equations of a Parabola

Deriving the equations of a parabola involves using the definition of a parabola and applying algebraic manipulation. By considering the distances between a point on the parabola and the focus, and the directrix, you can derive the standard form of the parabola’s equation. This can then be manipulated to form the vertex or factored forms.

## Writing Equations of a Parabola in Standard Form

Writing the equation of a parabola in standard form involves knowing the vertex (h, k) and the value of p (the distance from the vertex to the focus or from the vertex to the directrix). For a vertical parabola, the standard form is (x-h)² = 4p(y-k), and for a horizontal parabola, it’s (y-k)² = 4p(x-h).

## Solving Problems involving Parabolas

Parabolas are a common feature in many mathematical problems, especially in fields such as physics, engineering, and calculus. Solving these problems typically involves understanding the properties of parabolas, such as their vertex, focus, and directrix, and using these to write and solve equations. Strategies include graphing the parabola, factoring its equation, and applying calculus methods such as differentiation.

## Applications of Parabolas

Parabolas have a wide range of applications in the real world. They feature in physics, where projectile motion follows a parabolic path. In engineering, parabolic shapes are used in the design of car headlights, satellite dishes, and bridges due to their unique reflective and structural properties. Even in nature, parabolic shapes are found, such as in the paths of comets around the sun.

## Practice Problems on Parabolas

Let’s enhance our understanding of parabolas with some practice problems.

Problem 1: Find the vertex, focus, and directrix of the parabola given by the equation (x-3)² = 4(y-2).

Problem 2: Given a parabola with a focus at (6,8) and a directrix of y = 4, write the equation of the parabola in standard form.

Problem 3: If a parabola opens upwards and has its vertex at the origin (0,0), and the focus is at the point (0,2), what is its standard form equation?

Problem 4: Graph the parabola given by the equation y = x² – 4x + 4. Label the vertex and axis of symmetry.

Problem 5: A bridge is built in the shape of a parabolic arch. The bridge is 30 meters wide, and at the center, the arch is 10 meters high. Find the equation of the parabola, assuming the vertex is at the origin and it opens upward.

Problem 6: A water fountain’s stream forms a parabolic shape. The water reaches a maximum height of 5 m when the horizontal distance is 2 m. What is the equation of the parabola describing the water’s path if we ignore air resistance?

Try to solve these problems to get a practical sense of how parabolas work. Understanding how to manipulate their equations and properties will provide you with a powerful mathematical tool.

## Conclusion

And there we have it, a comprehensive dive into the captivating world of parabolas. We hope this exploration, courtesy of Brighterly, has illuminated the significance of this powerful mathematical concept for you. From its definition, core properties to its real-life applications, parabolas serve as an excellent testament to the beauty and practicality of mathematics.

Parabolas aren’t just abstract figures confined to a textbook. They are mathematical phenomena deeply woven into the fabric of our universe. As we’ve seen, their reach extends to physics, engineering, and even the nature around us.

Remember, every parabolic curve you see, whether it’s a soaring baseball, a graceful arch bridge, or a humble satellite dish, reflects the profound influence of parabolas on our world. And as always, Brighterly is here to illuminate your path of discovery, making mathematics a brighter journey. So stay curious, keep exploring, and let’s continue this exciting mathematical journey together!

## Frequently Asked Questions on Parabolas

### What is the importance of the vertex of a parabola?

The vertex of a parabola is the point where the parabola changes direction. It’s significant because it’s the highest or lowest point on the graph of the parabola, making it a crucial point in many mathematical and real-world problems.

### What does the focus of a parabola represent?

The focus of a parabola is a fixed point inside the curve. It has a unique property: any point on the parabola is equidistant from the focus and the directrix (a fixed line outside the curve). This property is fundamental in defining the parabola and its applications, particularly in optics and signal processing.

### How does the value of ‘p’ in a parabola’s equation affect its graph?

The value of ‘p’ in a parabola’s equation is the distance from the vertex to the focus or from the vertex to the directrix. The sign of ‘p’ determines the direction in which the parabola opens: if p > 0, a vertical parabola opens upward, and a horizontal parabola opens to the right; if p < 0, a vertical parabola opens downward, and a horizontal parabola opens to the left. The absolute value of ‘p’ affects the ‘width’ of the parabola — larger values of |p| result in a ‘narrower’ parabola.