Dot Product – Formula, Definition With Examples

Hello Brighterly learners, the masters of math in making! Today, we are going to talk about an important concept in vector algebra – the dot product or scalar product. Understanding the dot product can open up a world of understanding in fields ranging from physics to computer science, and even in more complex math topics. So, are you ready to take another step on your journey to becoming math maestros? Let’s dive into the world of dot products!

What is a Dot Product?

The dot product, also known as the scalar product, is a binary operation that combines two vectors to produce a scalar. Picture it as a method to multiply vectors, resulting in a single number. So, you can think of it as an operation that takes two equal-length sequences of numbers and returns a single number. This characteristic makes it unique from the cross product, which combines two vectors to produce another vector. This simplicity in interpretation is what makes the dot product such a fundamental concept in vector calculus, physics, and engineering.

Definition of Scalar Product

The scalar product of two vectors can be defined as the product of the magnitudes (or lengths) of the two vectors and the cosine of the angle between them. This mathematical operation is commutative, meaning the order in which the vectors are multiplied doesn’t affect the result. It’s also distributive over vector addition, which we’ll further dive into in the following sections. Interestingly, the scalar product is known as the dot product in the English-speaking world due to the dot symbol often used to denote it.

Definition of Dot Product

The dot product is essentially the same as the scalar product, just by a different name. It is the sum of the products of the corresponding entries of the two sequences of numbers. With a geometric interpretation, the dot product is equal to the length of one vector times the length of the shadow of the second vector upon the first. Or vice versa, demonstrating its commutative nature. To put it in simple terms, it is a way of multiplying vectors together, with the result being a scalar.

Properties of Scalar and Dot Products

Both the scalar product and dot product share the same properties due to their inherent similarity. They have specific properties that allow them to perform various mathematical and physical computations.

Properties of Scalar Product

  1. Commutativity: The scalar product of two vectors is commutative. That is, the order in which vectors are multiplied does not affect the final scalar product.
  2. Distributivity: The scalar product is distributive over vector addition. Meaning, when a vector is multiplied (dot product) with the addition of two other vectors, the result is the same as if the vector was multiplied individually with the other vectors and then added.
  3. Associativity with Real Numbers: The scalar product is associative with real numbers. In other words, a scalar multiple of a dot product results in the same value as the dot product of the scalar multiple of a vector.

Properties of Dot Product

The dot product shares all of its properties with the scalar product as they are essentially the same concept. So the properties of dot product include commutativity, distributivity over vector addition, and associativity with real numbers, just like the scalar product.

Difference Between Scalar Product and Dot Product

As previously mentioned, there is no actual difference between the scalar product and the dot product. They are simply two different names for the same operation in vector algebra. The term scalar product is often used in more formal, mathematical environments, while dot product is commonly used in engineering and physics.

Formulas of Scalar and Dot Products

It is critical to understand the formulas of scalar and dot products to implement these operations effectively.

Writing Formulas of Scalar Product

The formula for the scalar product is straightforward: If we have two vectors, A = (a1, a2) and B = (b1, b2), the scalar product is defined as:

A . B = a1*b1 + a2*b2

This formula can be expanded for vectors with more dimensions.

Writing Formulas of Dot Product

Since the dot product is the same as the scalar product, the formula is identical:

A . B = a1*b1 + a2*b2

This formula also applies to vectors of more than two dimensions, where each corresponding pair of elements is multiplied together, and the results are summed.

Practice Problems on Scalar and Dot Products

Practicing problems is indeed the best way to solidify the understanding of scalar and dot products. Let’s take a closer look at a few examples to understand these concepts better.

  1. Example Problem 1

Let’s say we have two vectors:

A = (3, 4)
B = (2, -1)

We want to calculate the dot product of these two vectors.

A . B = 3*2 + 4*(-1)
      = 6 - 4
      = 2

So, the dot product (or scalar product) of vectors A and B is 2.

  1. Example Problem 2

Now, let’s try a three-dimensional vector. Consider the following vectors:

A = (1, 2, 3)
B = (4, -5, 6)

We calculate the dot product in the same way, by multiplying corresponding elements and summing the results.

A . B = 1*4 + 2*(-5) + 3*6
      = 4 - 10 + 18
      = 12

Therefore, the dot product of vectors A and B is 12.

  1. Example Problem 3

Finally, we’ll consider a case where the dot product is zero. For example:

A = (1, 1)
B = (1, -1)

Again, we calculate the dot product:

A . B = 1*1 + 1*(-1)
      = 1 - 1
      = 0

A dot product of zero is especially interesting because it tells us that the two vectors are orthogonal (i.e., they are at right angles to each other). This has important implications in physics and computer graphics.


Dear Brighterly learners, you’ve done an amazing job exploring the world of dot products! We began our journey by understanding the basics of the dot product and scalar product, and discovered that they’re actually the same thing! We then moved on to grasp their properties, explore the difference (or lack thereof) between the two, and dive into their formulas.

Your adventurous spirit took us further, and we practiced some problems on scalar and dot products, reinforcing the concept in a practical and hands-on way. We hope that these exercises will encourage you to keep practicing and become comfortable with these mathematical operations.

Remember, every math concept you conquer, including the dot product, brings you one step closer to unlocking the mysteries of the universe, as math is the language it speaks. So keep exploring, keep asking questions, and keep learning. At Brighterly, we are proud of your progress and are always here to help light up your path of learning. Till next time, happy learning!

Frequently Asked Questions on Scalar and Dot Products

Is there a difference between the dot product and the scalar product?

No, there is no difference between the dot product and the scalar product. They are just two different names for the same operation in vector algebra. They both take in two vectors and produce a scalar. They share the same properties of commutativity, distributivity over vector addition, and associativity with real numbers. The different terms are used interchangeably depending on the field or region, with the term “dot product” being more common in English-speaking regions due to the dot symbol used to denote it.

Where is the dot product used?

The dot product finds its uses in a wide range of fields, from physics to computer science and engineering. It’s commonly used to determine the angle between two vectors, find the length of a vector, or calculate the projection of one vector onto another. In computer graphics, it’s used to calculate lighting and shading. In physics, it helps in work calculations. The dot product’s wide applications make it an essential tool in many scientific calculations.

Why is it called the scalar product?

It’s called the scalar product because the result of the operation is a scalar (a single number) as opposed to a vector. The operation essentially scales or modifies one vector according to the magnitude and direction of another, resulting in a single scalar quantity.

Information Sources:
  1. Wikipedia: Dot Product
  2. Mathworld – Dot Product
  3. Brilliant: Dot Product

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