Is the affine cipher e(x) = 13x + 9 (mod 63) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus) if no, explain why. Is the affine cipher e(x) = 22x + 10 (mod 63) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus), if no, explain why.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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**Learning Target N5**: *I can encode English sentences into numbers and reverse the process. I can perform basic affine ciphers and find decryption functions. I can correctly state why an affine cipher is or is not invertible.*

1. Is the affine cipher \( e(x) = 13x + 9 \pmod{63} \) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus); if no, explain why.

2. Is the affine cipher \( e(x) = 22x + 10 \pmod{63} \) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus); if no, explain why.
Transcribed Image Text:**Learning Target N5**: *I can encode English sentences into numbers and reverse the process. I can perform basic affine ciphers and find decryption functions. I can correctly state why an affine cipher is or is not invertible.* 1. Is the affine cipher \( e(x) = 13x + 9 \pmod{63} \) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus); if no, explain why. 2. Is the affine cipher \( e(x) = 22x + 10 \pmod{63} \) invertible? Yes or no. If yes, find the inverse (fully reduced with positive terms modulo the modulus); if no, explain why.
**Transcription for Educational Website**

**Topic: Modular Arithmetic and Inverses**

1. Since \( \gcd(9, 63) = 9 \neq 1 \), not invertible.

2. \( \gcd(10, 63) = 1 \), so it is invertible.

   \[ 10^{-1} \equiv 19 \, (\text{mod} \, 63) \]

   So,

   \[
   x \equiv 10y + 17 \, (\text{mod} \, 63)
   \]

   \[
   x - 17 \equiv 10y \, (\text{mod} \, 63)
   \]

   \[
   \Rightarrow 19x - 323 = y \, (\text{mod} \, 63)
   \]

   So, 

   \[
   e^{-1}(x) = 19x + 55 \, (\text{mod} \, 63)
   \]

**Explanation:**

This text explores the concepts of modular arithmetic and the conditions under which a number is invertible. The key focus is on determining when a modular inverse exists, using examples and calculations for clarity. In this example, the greatest common divisor (GCD) is used to determine invertibility.
Transcribed Image Text:**Transcription for Educational Website** **Topic: Modular Arithmetic and Inverses** 1. Since \( \gcd(9, 63) = 9 \neq 1 \), not invertible. 2. \( \gcd(10, 63) = 1 \), so it is invertible. \[ 10^{-1} \equiv 19 \, (\text{mod} \, 63) \] So, \[ x \equiv 10y + 17 \, (\text{mod} \, 63) \] \[ x - 17 \equiv 10y \, (\text{mod} \, 63) \] \[ \Rightarrow 19x - 323 = y \, (\text{mod} \, 63) \] So, \[ e^{-1}(x) = 19x + 55 \, (\text{mod} \, 63) \] **Explanation:** This text explores the concepts of modular arithmetic and the conditions under which a number is invertible. The key focus is on determining when a modular inverse exists, using examples and calculations for clarity. In this example, the greatest common divisor (GCD) is used to determine invertibility.
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