(a) Find an inverse for 73 modulo 660. First use the extended Euclidean algorithm to find the greatest common divisor of 660 and 73 and express it as a linear combination of 660 and 73. Step 1: Find q, and r, so that 660 - 73 -4, + where Osr, <73. Then r,- 660 - 73 - 4,- Step 2: Find q, and r, so that 73 -9+ where 0sr Then r,-73- Step 3: Find and so that 1-24+ where osr <- Then, 4, -0 Step 4: Select the comrect statement from the options below. O Becauser-0, god (660, 73) - 73 -r,4,-1. O Because r,- 0, god (660, 73) -- - O Becauser- 1, god (660, 73) - 73 - 2-0. O Because r - 1, god (660, 73)--73-4-0. O Becauser- 1, god (660, 73) -- -0. Next, substitute numerical values backward through the preceding steps, simplifying the results for each step, to find god (660, 73) -1- 660s + 73r, where s- and t- It follows that 73 - (0 =1 (mod 660), and so |is an inverse for 73 modulo 660. (b) Find the least positive solution for the congruence: 73x = 125 (mod 660). Step 1: By part (a), 73 0) =1 (mad 660). Multiply both sides by 125 to obtain 73 - 125 =1- 125 (mad 660) = 125 (mod 660). Let x- 125- Then 73x = 125 (mod 660). Nate that x is a solution to the given congruence, but it may not be the least positive solution. Step 2 Let v be the remainder abtained when x is divided by 660. Then v- Jand, by Theorem 8.4.1 and Theorem 8.4.3, 73x = 73v (mod 660). Hence, v is also a solution to the congruence. In other words, 73v = 125 (mod 660). Suppose u is any positive solution to the congruence that is less than or equal to v. Then 73- u= 73 - J(mad 660). Since 73 is prime, gdc(73, 660) - 1. Thus, Selec- can be applied to conclude that u- Therefore, is the least positive solution to the congruence.

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Chapter2: Second-order Linear Odes
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Certainly! Below is a transcription of the text from the image with explanations that would fit an educational website.

---

### Finding an Inverse for 73 modulo 660

#### (a)

**Objective:** Find an inverse for 73 modulo 660.

1. **First Step:** Use the extended Euclidean algorithm to find the greatest common divisor (gcd) of 660 and 73, expressing it as a linear combination of 660 and 73.

   - **Step 1:** Find \( q_1 \) and \( r_1 \) such that:
     \[
     660 = 73 \times q_1 + r_1, \quad \text{where } 0 \leq r_1 < 73.
     \]
     Then, \( r_1 = 660 - 73 \times q_1 \).

   - **Step 2:** Find \( q_2 \) and \( r_2 \) so that:
     \[
     73 = r_1 \times q_2 + r_2, \quad \text{where } 0 \leq r_2 < r_1.
     \]
     Then, \( r_2 = 73 - r_1 \times q_2 = \_\_\_\_\_\_ \).

   - **Step 3:** Find \( q_3 \) and \( r_3 \) so that:
     \[
     r_1 = r_2 \times q_3 + r_3, \quad \text{where } 0 \leq r_3 < r_2.
     \]
     Then, \( r_3 = \_\_\_\_\_ - (\_\_\_\_\_\_\_) \times q_3 = \_\_\_\_\_\_ \).

2. **Step 4:** Select the correct statement from the options below.
   - Because \( r_3 = 0 \), gcd (660, 73) = \( r_2 = r_1 - q_3 \times q_2 = 1 \).
   - ...

Next, substitute numerical values backward through the preceding steps, simplifying the results for each step to find gcd (660, 73) = 1 = 660s + 73t, where \( s = \_\_\_\_\_\_ \) and \( t = \_\_\_\
Transcribed Image Text:Certainly! Below is a transcription of the text from the image with explanations that would fit an educational website. --- ### Finding an Inverse for 73 modulo 660 #### (a) **Objective:** Find an inverse for 73 modulo 660. 1. **First Step:** Use the extended Euclidean algorithm to find the greatest common divisor (gcd) of 660 and 73, expressing it as a linear combination of 660 and 73. - **Step 1:** Find \( q_1 \) and \( r_1 \) such that: \[ 660 = 73 \times q_1 + r_1, \quad \text{where } 0 \leq r_1 < 73. \] Then, \( r_1 = 660 - 73 \times q_1 \). - **Step 2:** Find \( q_2 \) and \( r_2 \) so that: \[ 73 = r_1 \times q_2 + r_2, \quad \text{where } 0 \leq r_2 < r_1. \] Then, \( r_2 = 73 - r_1 \times q_2 = \_\_\_\_\_\_ \). - **Step 3:** Find \( q_3 \) and \( r_3 \) so that: \[ r_1 = r_2 \times q_3 + r_3, \quad \text{where } 0 \leq r_3 < r_2. \] Then, \( r_3 = \_\_\_\_\_ - (\_\_\_\_\_\_\_) \times q_3 = \_\_\_\_\_\_ \). 2. **Step 4:** Select the correct statement from the options below. - Because \( r_3 = 0 \), gcd (660, 73) = \( r_2 = r_1 - q_3 \times q_2 = 1 \). - ... Next, substitute numerical values backward through the preceding steps, simplifying the results for each step to find gcd (660, 73) = 1 = 660s + 73t, where \( s = \_\_\_\_\_\_ \) and \( t = \_\_\_\
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