Linear Diophantine Equations

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Questions and Answers

Which condition must be met for the equation $ax + by = c$ to be considered a linear Diophantine equation (LDE)?

  • Coefficients $a$, $b$, and $c$ can be rational numbers, and solutions for $x$ and $y$ must be integers.
  • Coefficients $a$, $b$, and $c$ must be integers, and solutions for $x$ and $y$ can be any real number.
  • Coefficients $a$, $b$, and $c$ can be any real number, but solutions for $x$ and $y$ must be integers.
  • Coefficients $a$, $b$, and $c$ must be integers, and solutions for $x$ and $y$ must also be integers. (correct)

Given the equation $5x + 8y = c$, for what values of $c$ will this equation NOT have integer solutions?

  • When $c$ is not divisible by the greatest common divisor of 5 and 8. (correct)
  • When $c$ is a multiple of 8.
  • When $c$ is a prime number.
  • When $c$ is a multiple of 5.

Which of the following statements correctly describes the condition for a linear Diophantine equation $ax + by = c$ to have a solution?

  • A solution exists only if the greatest common divisor of $a$ and $b$ divides $c$. (correct)
  • A solution exists only if $c$ is divisible by the least common multiple of $a$ and $b$.
  • A solution exists only if $c$ is a multiple of both $a$ and $b$.
  • A solution exists only if $a$, $b$, and $c$ are all prime numbers.

Which of the following equations does NOT have an integral solution?

<p>$5x + 10y = 16$ (B)</p> Signup and view all the answers

If the greatest common divisor of $a$ and $b$ does not divide $c$ in the equation $ax + by = c$, what can be concluded?

<p>The equation has no integer solutions. (B)</p> Signup and view all the answers

What does it mean for a linear Diophantine equation to be 'solvable'?

<p>It means that the equation has a solution in integers. (A)</p> Signup and view all the answers

What is the first step in solving a linear Diophantine equation?

<p>Verify that the solutions exist, i.e., check if $gcd(a, b)$ divides $c$. (C)</p> Signup and view all the answers

After confirming that an LDE $ax + by = c$ is solvable, what is the next step in finding its solutions?

<p>Use the Euclidean Algorithm to find $d = gcd(a, b)$. (A)</p> Signup and view all the answers

How is the Euclidean Algorithm used when solving linear Diophantine equations?

<p>To find the greatest common divisor (gcd) of the coefficients $a$ and $b$. (A)</p> Signup and view all the answers

After finding $d = gcd(a, b)$ using the Euclidean Algorithm, what is the next step in solving the LDE $ax + by = d$?

<p>Find $x_0$ and $y_0$ such that $ax_0 + by_0 = d$. (D)</p> Signup and view all the answers

How do you find $x_0$ and $y_0$ such that $ax_0 + by_0 = d$ after using the Euclidean Algorithm?

<p>By going backward through the steps of the Euclidean Algorithm. (C)</p> Signup and view all the answers

Given $ax_0 + by_0 = d$, where $d = gcd(a, b)$, how can the general solutions for the LDE $ax + by = c$ be expressed?

<p>$x = (c/d)x_0 + (b/d)t$, $y = (c/d)y_0 - (a/d)t$, where $t$ is an integer. (D)</p> Signup and view all the answers

In the general solutions $x = (c/d)x_0 + (b/d)t$ and $y = (c/d)y_0 - (a/d)t$ for an LDE, what does the parameter $t$ represent?

<p>Any integer that generates infinitely many solutions. (C)</p> Signup and view all the answers

How are particular solutions obtained from the general solutions of a linear Diophantine equation?

<p>By choosing specific integer values for the parameter $t$ in the general solutions. (C)</p> Signup and view all the answers

To find positive solutions for a LDE, after determining the general solution, what is the next step?

<p>Set $x &gt; 0$ and $y &gt; 0$, then solve the resulting inequalities for the parameter $t$. (B)</p> Signup and view all the answers

What does the expression '$-5.1 < t < -4.86$' indicate when solving for positive solutions of a linear Diophantine equation?

<p>There are no integer values of $t$ that satisfy both $x &gt; 0$ and $y &gt; 0$. (A)</p> Signup and view all the answers

What is the first step in solving a word problem involving linear Diophantine equations?

<p>Represent the unknown values using variables. (C)</p> Signup and view all the answers

After representing the unknown values with variables in a word problem, what should you do next?

<p>Formulate an equation based on the conditions provided in the problem. (B)</p> Signup and view all the answers

After forming an LDE from a word problem, what is the next step in finding the solution?

<p>Solve the resulting LDE using appropriate methods. (B)</p> Signup and view all the answers

Once the LDE is solved, what is the final step in solving a word problem involving Diophantine equations?

<p>Convert the integer solutions back into the context of the original problem. (B)</p> Signup and view all the answers

Consider the equation $9x + 15y = 27$. Which of the following statements is true?

<p>The equation has an infinite number of integer solutions because $gcd(9, 15) = 3$ and 3 divides 27. (A)</p> Signup and view all the answers

Suppose you need to divide 100 coins between two people such that one receives an amount that is a multiple of 7 and the other receives an amount that is a multiple of 5. This can be represented by $5x + 7y = 100$. What does 'solving this LDE' accomplish in context?

<p>Find how many coins each person receives. (D)</p> Signup and view all the answers

Given the LDE $12x + 18y = 30$, which of the following is a valid first step in finding the general solution?

<p>Simplify the equation to $2x + 3y = 5$ by dividing all terms by 6. (A)</p> Signup and view all the answers

Which of the following linear Diophantine equations is guaranteed to have integer solutions?

<p>$16x + 24y = 48$ (A)</p> Signup and view all the answers

For the linear Diophantine equation $6x + 10y = c$, what values of $c$ would allow for integer solutions?

<p>Any multiple of 2. (A)</p> Signup and view all the answers

Consider the linear Diophantine equation $ax + by = c$. If $gcd(a, b) = 1$, which of the following statements must be true?

<p>The equation always has integer solutions. (D)</p> Signup and view all the answers

A farmer sells chickens and ducks. Each chicken costs $5 and each duck costs $3. If a person spends exactly $52, what equation represents the number of chickens ($x$) and ducks ($y$) purchased?

<p>$5x + 3y = 52$ (D)</p> Signup and view all the answers

Is the Diophantine equation $14x + 49y = 150$ solvable?

<p>No, because the greatest common divisor of 14 and 49 does not divide 150. (B)</p> Signup and view all the answers

Suppose $x = 3 + 5t$ and $y = 2 - 4t$ are the general solutions to a linear Diophantine equation. What happens to the values of x and y as t increases?

<p>$x$ increases and $y$ decreases. (D)</p> Signup and view all the answers

A baker is making cakes and cookies. Cakes require 3 cups of flour and cookies require 1 cup of flour. If the baker has 20 cups of flour, the situation can be modeled by the equation $3x + y = 20$. What does $x$ represent in this context?

<p>The number of cakes baked. (D)</p> Signup and view all the answers

If a store sells apples for $2 each and bananas for $1 each and someone spends exactly $15, which equation models the number of apples ($x$) and bananas ($y$) bought?

<p>$2x + y = 15$ (A)</p> Signup and view all the answers

Determine which of the following Diophantine equations has no solution.

<p>$7x + 14y = 3$ (D)</p> Signup and view all the answers

What is the solution to $2x + 5y = 16$ if $x = 3$?

<p>y = 2 (A)</p> Signup and view all the answers

What is the general solution to the Diophantine equation $5x + 10y = 25$?

<p>$x = 5 - 2t, y = t$ (C)</p> Signup and view all the answers

What is a valid integer solution to the Diophantine equation $2x + 3y = 7$?

<p>x = 3, y = 1 (C)</p> Signup and view all the answers

What is the value of t if x = 1 in the Diophantine equation $x = 1 + 4t$?

<p>0 (A)</p> Signup and view all the answers

What is the value of $gcd(17, 23)$?

<p>1 (B)</p> Signup and view all the answers

Which of the following is needed to find the general solution from the particular solution?

<p>Using the Euclidean Algorithm (C)</p> Signup and view all the answers

If an integer $t$ has the following range $-3.2 < t < -1.2$, How many integers fit in this range?

<p>2 (B)</p> Signup and view all the answers

Flashcards

What is a Linear Diophantine Equation (LDE)?

ax + by = c where a, b, and c are integers, and solutions must also be integers.

When does ax + by = c have NO solution?

The equation ax + by = c has no integral solution if the greatest common divisor of a and b does not divide c.

What if ax + by = c has a solution?

If ax + by = c has a solution, then the greatest common divisor of a and b divides c.

Steps for Solving LDE

First, test for solutions. Then, use the Euclidean Algorithm to find d = (a, b). Find x₀ and y₀ such that ax₀ + by₀ = d and apply formulas.

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Word problems in LDE

unknown values using two variables.

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Next step after identifying unknowns

Use the conditions given to form the equation

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The next step

Solve the equation after substituting the conditions given using the method discussed

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The Final Step

Find the solution/s to the problem using the results in step 3.

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Study Notes

  • Linear Diophantine Equations (LDE) involve:
  • Definition
  • Finding Solutions
  • Solving Word Problems Involving them

Definition of LDE

  • For a, b, and c ∈ Z, ax + by = c signifies a linear diophantine equation if its solutions require integers.
  • Example: 2x + 3y = 5 has (1, 1) and (-2, 3) as solutions, but not (-1/2, 2).
  • ax + by = c has NO solution if (a, b) does not divide c.
  • If ax + by = c has a solution, then (a, b) divides c.

Determining Integral Solutions in LDE

  • Example: Determining whether Linear Diophantine Equations have an integral solution includes finding (a, b).
  • 2x + 7y = 1, (2, 7) = 1, since 1|1, there is an integral solution
  • 7x + 13y = 1, (7, 13) = 1, since 1|1, there is an integral solution
  • 3x + 6y = 4, (3, 6) = 3, since 3 does not divide 4, there is NO integral solution
  • Example:
  • 5x + 22y = 18, (5, 22) = 1, since 1|18, there is an integral solution
  • 6x + 64y = 2, (6, 64) = 2, since 2|2, there is an integral solution
  • 9x + 30y = 5, (9, 30) = 3, since 3 does not divide 5, there is NO integral solution

Finding Solutions of LDE

  • If the LDE ax + by = c has an integral solution, it's solvable with infinitely many solutions.
  • Solutions are given by:
  • x = (c/d) * x₀ + (b/d) * t
  • y = (c/d) * y₀ - (a/d) * t
  • t ∈ Z, where d = (a, b), and x₀ and y₀ ∈ Z satisfying ax₀ + by₀ = d
  • These are called general solutions.

Steps in Solving LDE

  • Test if solutions exist, meaning (a, b)|c.
  • Use the Euclidean Algorithm to find d, where d = (a, b).
  • Find x₀ and y₀ so that ax₀ + by₀ = d (going backward).
  • Form the general solution by substituting a, b, c, d, x₀, and y₀ into the equations.
  • Find specific solutions by substituting integer values for t in the general solutions.
  • Identify positive solutions, if any, by setting general solutions x and y into inequalities x > 0 and y > 0.

Solving LDE: Example

  • Equation: 7x + 10y = 17
  • Step 1: (7,10) = 1, since 1|17, there is a solution.
  • Step 2: Using Euclidean Algorithm:
  • 10 = 7(1) + 3
  • 7 = 3(2) + 1
  • 3 = 1(3) + 0
  • Therefore, d = (7, 10) = 1
  • Step 3: Going backward:
  • 1 = 7(1) – 3(2)
  • 1 = 7 – (10 – 7) (2)
  • 1 = 7(3) + 10(-2)
  • Therefore, x₀ = 3 and y₀ = -2
  • Step 4: Find the general solution:
  • x = (17/1)(3) + (10/1)t = 51 + 10t, t ∈ Z
  • y = (17/1)(-2) - (7/1)t = -34 - 7t, t ∈ Z
  • Step 5: Find particular solutions by letting t as any integer:
  • if t = 0: x = 51 + 10(0) = 51, y = -34 - 7(0) = -34
  • if t = 1: x = 51 + 10(1) = 61, y = -34 + 7(1) = -34
  • if t = -1: x = 41, y = -27
  • Step 6: Find all positive solutions:
  • x > 0 :51 + 10t > 0 → 10t > -51 → t > -5.1
  • y > 0 : -34 - 7t > 0 → -7t > 34 → t < -4.86
  • -5.1 < t < -4.86, where t is any integer that satisfies the two inequalities. if t = -5, then x = 51 + 10(-5) = 1 and y = -34 - 7(-5) = 1

Steps for Word Problems Involving Linear Diophantine Equations

  • Represent the unknowns using two variables.
  • Form the equation based on the problem conditions.
  • Solve the LDE using the discussed methods.
  • Find the solutions to the problem using Step 3.

Example Word Problem

  • Five times a positive integer, added to seven times another positive integer, gives 100; find all integral solutions.

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