Problem 9 - Differential Equations and Linear Algebra

Question

Verify the commutative law of addition for vectors in \(\mathbb{R}^{4}\).

Step-by-Step Solution

Answer

For arbitrary vectors \(u = (u_1, u_2, u_3, u_4)\) and \(v = (v_1, v_2, v_3, v_4)\) in \(\mathbb{R}^{4}\), we computed their sums as \(u+v = (u_1 + v_1, u_2 + v_2, u_3 + v_3, u_4 + v_4)\) and \(v+u = (v_1 + u_1, v_2 + u_2, v_3 + u_3, v_4 + u_4)\). Since their corresponding entries are equal, we have \(u+v = v+u\). Thus, the commutative law of addition for vectors in \(\mathbb{R}^{4}\) is verified.

Step 1: Declare Vectors u and v

Let \(u = (u_1, u_2, u_3, u_4)\) and \(v = (v_1, v_2, v_3, v_4)\) be two vectors in \(\mathbb{R}^{4}\). Now, we will find the sum of these vectors to check whether the commutative law of addition holds.

Step 2: Compute u+v

By definition of vector addition, we have \(u+v = (u_1 + v_1, u_2 + v_2, u_3 + v_3, u_4 + v_4)\).

Step 3: Compute v+u

Similarly, we can find the sum of vectors v and u as \(v+u = (v_1 + u_1, v_2 + u_2, v_3 + u_3, v_4 + u_4)\). Now, we will check if these two sums are equal to verify the commutativity.

Step 4: Compare u+v and v+u

Comparing the entries of vectors \(u+v\) and \(v+u\), we can see that their corresponding entries are equal: \(u_1 + v_1 = v_1 + u_1\), \(u_2 + v_2 = v_2 + u_2\), \(u_3 + v_3 = v_3 + u_3\), \(u_4 + v_4 = v_4 + u_4\). So, we have \(u+v = (u_1 + v_1, u_2 + v_2, u_3 + v_3, u_4 + v_4) = (v_1 + u_1, v_2 + u_2, v_3 + u_3, v_4 + u_4) = v+u\). We have shown that \(u+v = v+u\) holds for any vectors \(u, v \in \mathbb{R}^{4}\). Therefore, the commutative law of addition for vectors in \(\mathbb{R}^{4}\) is verified.

Key Concepts

Vector Addition in R^4

Understanding vector addition within the realm of four-dimensional space, denoted as \(\mathbb{R}^{4}\), is a fundamental concept in linear algebra. Just as in two or three dimensions, vectors in \(\mathbb{R}^{4}\) are added by combining their corresponding components. A vector in \(\mathbb{R}^{4}\) is represented as a tuple of four real numbers, for example, \(u = (u_1, u_2, u_3, u_4)\).

To perform vector addition, simply add the respective components from each vector. The result is a new vector in \(\mathbb{R}^{4}\), \(w = (w_1, w_2, w_3, w_4)\), where each \(w_i = u_i + v_i\) for \(i = 1, 2, 3, 4\). This operation is used extensively in physics, engineering, and other sciences to represent and solve problems involving forces, velocities, and other vector quantities in multi-dimensional space.

Linear Algebra Principles

Linear algebra is the branch of mathematics that deals with vectors, vector spaces, linear transformations, and systems of linear equations. Principles of linear algebra are based on a set of axioms which vector spaces must satisfy. Among these, the crucial properties relevant to our exercise are the properties of vector addition.

Vector addition is associative and commutative, which means that the order in which vectors are added does not change the result. This is critical when verifying the commutative law for vector addition as demonstrated in the exercise. It's also important to note that there exists a zero vector in \(\mathbb{R}^{4}\) such that when any vector is added to it, the original vector is unchanged. These principles are not just theoretical—they have practical applications in fields as varied as computer graphics, quantum mechanics and economics.

Proof of Vector Properties

In proving properties of vectors, such as the commutative law of vector addition, we rely on fundamental properties of real numbers. The commutative property of real number addition, which states that the sum remains the same regardless of the order of the addends, \(a + b = b + a\), underpins the proof for vector addition.

When we add vectors component-wise, as we do in any \(\mathbb{R}^{n}\) space, we are essentially performing multiple real number additions. Therefore, the proof of properties like commutativity boils down to applying these well-established number properties to each component of the vectors. This connection between real number properties and vector operations is a powerful tool, allowing us to extend our intuition and understanding from basic arithmetic to higher-dimensional spaces.