Calculate A, where A = [2-i 3+2i 4 -i Calculate 2-4i|. Prove that for any complex numbers x and y, (xy) = (x)(y) and x+y=x+y.

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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### Problem 10

#### Complex Conjugate and Modulus

The **conjugate** of a complex number \( z = a + bi \) is \( a - bi \). We denote the conjugate by \( \overline{z} \).

We also define the **modulus** of a complex number \( z \), denoted by \( |z| \), as \( \sqrt{z\overline{z}} \). Note that \( z \overline{z} \) is always a nonnegative real number, so this is also a nonnegative real number.

#### Matrix Conjugate

Let \( A \) be a complex \( n \times n \) matrix, where \( n \ge 2 \). We define the matrix \( \overline{A} \) to be the matrix obtained by taking the conjugate of every entry of \( A \).

#### Questions

a. Calculate \( \overline{A} \), where \( A = \begin{bmatrix} 2 - i & 3 + 2i \\ 4 & -i \end{bmatrix} \).

b. Calculate \( |2 - 4i| \).

c. Prove that for any complex numbers \( x \) and \( y \), \( \overline{xy} = \overline{x} \overline{y} \) and \( \overline{x + y} = \overline{x} + \overline{y} \).

d. Prove that \( |yz| = |y||z| \) for any \( y, z \in \mathbb{C} \).

e. Prove that \( \det \overline{A} = \overline{\det A} \). (Hint: Show the \( 2 \times 2 \) case and use induction on \( n \).)

f. A **unitary matrix** \( A \in M_{n \times n}(\mathbb{C}) \) is one where \( \overline{A^T} = A^{-1} \). Prove that if \( A \) is a unitary matrix, then \( |\det A| = 1 \).

#### Explanations of Terms and Concepts

- **Complex Conjugate \( \overline{z} \)**: The conjugate of a complex number \( z = a
Transcribed Image Text:### Problem 10 #### Complex Conjugate and Modulus The **conjugate** of a complex number \( z = a + bi \) is \( a - bi \). We denote the conjugate by \( \overline{z} \). We also define the **modulus** of a complex number \( z \), denoted by \( |z| \), as \( \sqrt{z\overline{z}} \). Note that \( z \overline{z} \) is always a nonnegative real number, so this is also a nonnegative real number. #### Matrix Conjugate Let \( A \) be a complex \( n \times n \) matrix, where \( n \ge 2 \). We define the matrix \( \overline{A} \) to be the matrix obtained by taking the conjugate of every entry of \( A \). #### Questions a. Calculate \( \overline{A} \), where \( A = \begin{bmatrix} 2 - i & 3 + 2i \\ 4 & -i \end{bmatrix} \). b. Calculate \( |2 - 4i| \). c. Prove that for any complex numbers \( x \) and \( y \), \( \overline{xy} = \overline{x} \overline{y} \) and \( \overline{x + y} = \overline{x} + \overline{y} \). d. Prove that \( |yz| = |y||z| \) for any \( y, z \in \mathbb{C} \). e. Prove that \( \det \overline{A} = \overline{\det A} \). (Hint: Show the \( 2 \times 2 \) case and use induction on \( n \).) f. A **unitary matrix** \( A \in M_{n \times n}(\mathbb{C}) \) is one where \( \overline{A^T} = A^{-1} \). Prove that if \( A \) is a unitary matrix, then \( |\det A| = 1 \). #### Explanations of Terms and Concepts - **Complex Conjugate \( \overline{z} \)**: The conjugate of a complex number \( z = a
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