# Cross Product of Two Vectors – Definition With Examples

Created on Dec 31, 2023

Updated on January 9, 2024

Welcome to another insightful exploration at Brighterly, your trusted partner in making learning fun and approachable. Today we’ll delve into the fascinating world of vectors, specifically, the ‘Cross Product of Two Vectors’. This guide will cover everything from the basic definition to the more complex applications of this crucial concept in vector algebra. To supplement your learning, we’ve also included detailed examples and engaging practice problems. We believe in making mathematical concepts understandable and enjoyable for our young learners, so we’ve taken care to present this topic in a simple, yet engaging manner. Let’s dive right in!

## Definition of a Vector

Firstly, let’s define a vector. A vector is a mathematical entity that possesses both magnitude (its length) and direction. Unlike a scalar, which only has magnitude, vectors give us an intuitive way to describe movement and forces in space. For instance, if you’re playing a game of soccer, the ball’s direction and speed (magnitude) would be represented by a vector.

## Definition of the Cross Product

The cross product (also known as vector product) is a binary operation on two vectors in three-dimensional space. It results in a vector that is perpendicular (orthogonal) to the plane containing the original pair. The magnitude of this resulting vector corresponds to the area of the parallelogram formed by the two input vectors.

## Properties of Vectors

Vectors have certain properties that make them unique and practical to use. They can be added together, subtracted, and scaled (multiplied by scalars). Also, the length of a vector can be calculated using Pythagoras’ theorem in Euclidean space.

## Properties of the Cross Product

There are specific properties that define the operation of the cross product. First, it is anti-commutative, meaning swapping the order of vectors changes the result’s direction. Secondly, it is distributive over addition of vectors. Lastly, the cross product of parallel vectors is zero because they do not span a plane.

## Difference Between Dot Product and Cross Product

Vectors can be multiplied in two ways – the dot product and the cross product. While the dot product results in a scalar value, the cross product leads to another vector. Additionally, the dot product measures the extent to which two vectors point in the same direction, whereas the cross product measures the extent to which two vectors are perpendicular.

## Calculating the Cross Product of Two Vectors

The calculation of the cross product of two vectors involves the use of their components. Given two vectors a = [a1, a2, a3] and b = [b1, b2, b3], their cross product a × b is a vector [c1, c2, c3], where:

c1 = a2b3 – a3b2

c2 = a3b1 – a1b3

c3 = a1b2 – a2b1

To illustrate, let’s calculate the cross product of two vectors: a = [2, 3, 4] and b = [5, 6, 7].

c1 = 37 – 46 = 21 – 24 = -3

c2 = 45 – 27 = 20 – 14 = 6

c3 = 26 – 35 = 12 – 15 = -3

So, a × b = [-3, 6, -3].

## Writing Equations for the Cross Product

When expressing the cross product mathematically, if two vectors ‘a’ and ‘b’ are given as ‘a = ai + bj + ck’ and ‘b = di + ej + fk’, the cross product ‘a × b’ is:

a × b = (bf – ce)i – (af – cd)j + (ae – bd)k

This resulting vector is perpendicular (orthogonal) to the original plane containing ‘a’ and ‘b’. Its magnitude equals |a||b|sinθ, where |a| and |b| are the magnitudes of ‘a’ and ‘b’ respectively, and θ is the angle between them.

## Practice Problems on the Cross Product of Two Vectors

Let’s try a practice problem. Find the cross product of the vectors a = [1, 0, 0] and b = [0, 1, 0].

Using the formula for the cross product:

c1 = 00 – 01 = 0

c2 = 01 – 00 = 0

c3 = 11 – 00 = 1

So, a × b = [0, 0, 1].

Now try to calculate the cross product of a = [3, -3, 1] and b = [4, 9, 2] on your own. Remember, understanding the cross product of vectors provides valuable insights into the geometry of vectors and practicing these problems will help consolidate this understanding.

## Conclusion

We’ve reached the end of this exciting mathematical journey where we uncovered the intricacies of the ‘Cross Product of Two Vectors’. We hope this guide from Brighterly helped transform a complex subject into a manageable and enjoyable topic. The cross product is an essential concept in vector algebra with far-reaching implications in various fields including physics, engineering, and computer graphics. Understanding it is key to exploring more advanced mathematical topics and real-world phenomena. As always, we’re thrilled to be part of your learning journey, making math brighter, one concept at a time. Keep exploring, keep asking questions, and most importantly, keep enjoying the beautiful world of mathematics!

## Frequently Asked Questions on the Cross Product of Two Vectors

### What does the cross product tell us?

The cross product of two vectors gives us a new vector that is perpendicular to the plane containing the original vectors. Its direction follows the right-hand rule, and its magnitude is equal to the area of the parallelogram formed by the two vectors.

### What is the difference between the cross product and the dot product?

The dot product of two vectors gives a scalar quantity (a single number). It measures how much of one vector goes in the direction of the other. The cross product, on the other hand, gives a vector and shows how much the vectors are directed perpendicularly to each other.

### Can the cross product be zero? What does that imply?

Yes, the cross product can be zero. This occurs when the two input vectors are parallel or when at least one of the vectors is a zero vector. The zero cross product signifies that the vectors are not linearly independent, i.e., they do not define a plane in 3D space.

### How is the cross product used in real life?

The cross product has several real-life applications, especially in physics and engineering. For instance, it helps in calculating the torque exerted by a force (torque is the cross product of radius and force vectors). It’s also used in computer graphics to determine the surface normal of textures and polygons.

### Can we calculate the cross product for 2D vectors?

The cross product is technically only defined for 3D vectors. However, we can calculate something similar for 2D vectors by considering them as 3D vectors with a third component of zero. The result will be a new vector along the third dimension.