# 10 Differences Between dot product and cross product

## What is Dot Product?

The dot product, also known as the scalar product or inner product, is a mathematical operation that takes two vectors and produces a scalar quantity. It is defined by the product of the magnitudes of the vectors and the cosine of the angle between them.

### Examples of Dot Product

Let’s consider two vectors, A = [3, 4] and B = [5, 2]. The dot product of these vectors is calculated as follows:

A · B = (3 * 5) + (4 * 2) = 15 + 8 = 23

Thus, the dot product of A and B is 23.

### Uses of Dot Product

1. Finding the angle between two vectors: The dot product can be used to determine the angle between two vectors. By rearranging the dot product formula, we have cos(θ) = (A · B) / (|A| * |B|), where θ is the angle between the vectors.
2. Testing for orthogonality: Two vectors are orthogonal if and only if their dot product is zero. This property is useful in various applications, such as determining if two lines are perpendicular.
3. Calculating work done: In physics, the dot product is used to calculate the work done by a force acting on an object. The dot product of the force vector and the displacement vector gives the magnitude of the work done.

## What is Cross Product?

The cross product, also known as the vector product, is a mathematical operation that takes two vectors and produces a vector quantity perpendicular to both input vectors. It is defined as the product of the magnitudes of the vectors, the sine of the angle between them, and a unit vector perpendicular to the plane containing them.

### Examples of Cross Product

Consider two vectors, C = [2, 3, 4] and D = [5, 6, 7]. The cross product of these vectors is calculated as follows:

C × D = [(3 * 7) – (4 * 6), (4 * 5) – (2 * 7), (2 * 6) – (3 * 5)] = [−9, 6, −3]

Thus, the cross product of C and D is the vector [-9, 6, -3].

### Uses of Cross Product

1. Finding the direction of a normal vector: The cross product can be used to calculate the direction of the normal vector to a plane defined by two given vectors. This is essential in various fields, including computer graphics.
2. Calculating torque: In physics, the cross product is used to calculate torque, which is the twisting force applied to an object. The torque vector is obtained by taking the cross product of the position vector and the force vector.
3. Solving vector equations: The cross product is utilized in solving various vector equations and determining the solution space.

## Differences Table

Difference Area Dot Product Cross Product
Result Scalar Vector
Definition Multiplication of magnitudes and cosine of the angle Multiplication of magnitudes, sine of the angle, and perpendicular unit vector
Dimensionality Applicable to vectors in any dimension Only applicable to vectors in 3-dimensional space
Result Orientation No inherent direction, can be positive or negative Perpendicular to the plane formed by both input vectors
Orthogonality Two vectors are orthogonal if their dot product is zero Two vectors are orthogonal if their cross product is zero
Commutativity The dot product commutes: A · B = B · A The cross product does not commute: A × B = -(B × A)
Closure The dot product of two vectors results in a scalar within the same number system The cross product of two vectors results in a vector within the same number system
Calculation Complexity Relatively simpler to calculate More computationally intensive
Associativity The dot product is associative: (A · B) · C = A · (B · C) The cross product is not associative: (A × B) × C ≠ A × (B × C)
Inverse Operation Does not have a direct inverse operation Has a pseudo-inverse operation called the cross product with the inverse direction

### Conclusion

In summary, the dot product and cross product are both essential mathematical operations involving vectors. The dot product results in a scalar and is useful in determining angles, orthogonality, and work done. On the other hand, the cross product gives a vector perpendicular to the input vectors and finds applications in determining normal vectors, torque, and solving vector equations. Understanding the differences between these operations is crucial for their correct application in various fields of science and engineering.

Q: Can dot product or cross product be negative?
A: The dot product can be positive, negative, or zero, while the cross product does not have a negative value. It can only be zero or have a positive magnitude.

Q: How do you calculate the angle between two vectors using the dot product?
A: The angle θ between two vectors A and B can be calculated using the formula cos(θ) = (A · B) / (|A| * |B|), where · denotes the dot product and |A| and |B| represent the magnitudes of the vectors.

Q: When should I use the dot product?
A: The dot product is commonly used for calculating angles, testing orthogonality, and determining work done by a force.

Q: Can the dot product be zero if the magnitudes are non-zero?
A: Yes, the dot product can be zero if the angle between the vectors is 90 degrees, making them orthogonal.

Q: How do I calculate the cross product of two vectors?
A: To calculate the cross product of two vectors A and B, use the formula A × B = [ (Ay * Bz) – (Az * By), (Az * Bx) – (Ax * Bz), (Ax * By) – (Ay * Bx) ].