Math Problem Statement

show with steps

Find a pair of integers x and y such that 47x + 43y = gcd(47, 43).

Solution

We are tasked with solving the equation:

47x+43y=gcd(47,43)=147x + 43y = \gcd(47, 43) = 1

This is a linear Diophantine equation where the coefficients a=47a = 47, b=43b = 43, and the constant c=gcd(47,43)=1c = \gcd(47, 43) = 1.

We can solve it using the Extended Euclidean Algorithm to find integers xx and yy.


Step 1: Use the Euclidean Algorithm to find gcd(47,43)\gcd(47, 43)

The Euclidean Algorithm involves repeated division to find the remainder:

  1. 47÷4347 \div 43 gives quotient 11 and remainder:

    47143=447 - 1 \cdot 43 = 4

  2. Next, 43÷443 \div 4 gives quotient 1010 and remainder:

    43104=343 - 10 \cdot 4 = 3

  3. Then, 4÷34 \div 3 gives quotient 11 and remainder:

    413=14 - 1 \cdot 3 = 1

  4. Finally, 3÷13 \div 1 gives remainder 00, so:

    gcd(47,43)=1\gcd(47, 43) = 1

Now we backtrack to express 11 as a linear combination of 4747 and 4343.


Step 2: Back-substitution to express 11 as 47x+43y47x + 43y

We reverse the steps of the Euclidean Algorithm:

  1. From 413=14 - 1 \cdot 3 = 1, we write:

    1=4131 = 4 - 1 \cdot 3

  2. Substitute 33 using 4310443 - 10 \cdot 4 (from Step 2 of the Euclidean Algorithm):

    3=431043 = 43 - 10 \cdot 4

    Substituting into 1=4131 = 4 - 1 \cdot 3, we get:

    1=41(43104)1 = 4 - 1 \cdot (43 - 10 \cdot 4)

    Simplify:

    1=4143+1041 = 4 - 1 \cdot 43 + 10 \cdot 4

    Combine terms involving 44:

    1=1141431 = 11 \cdot 4 - 1 \cdot 43

  3. Substitute 44 using 4714347 - 1 \cdot 43 (from Step 1 of the Euclidean Algorithm):

    4=471434 = 47 - 1 \cdot 43

    Substituting into 1=1141431 = 11 \cdot 4 - 1 \cdot 43, we get:

    1=11(47143)1431 = 11 \cdot (47 - 1 \cdot 43) - 1 \cdot 43

    Simplify:

    1=114711431431 = 11 \cdot 47 - 11 \cdot 43 - 1 \cdot 43

    Combine terms involving 4343:

    1=114712431 = 11 \cdot 47 - 12 \cdot 43


Step 3: Identify the solution

We have expressed 11 as:

1=114712431 = 11 \cdot 47 - 12 \cdot 43

Thus, x=11x = 11 and y=12y = -12 is a solution.


Final Answer:

The pair (x,y)(x, y) is:

(x,y)=(11,12)(x, y) = (11, -12)


Let me know if you need further clarification or additional examples!


Related Questions:

  1. What are the steps of the Extended Euclidean Algorithm?
  2. How can we generalize solutions for linear Diophantine equations ax+by=cax + by = c?
  3. What happens if the gcd is not 11?
  4. Can we verify the solution 47x+43y=147x + 43y = 1 directly?
  5. How can we find additional solutions to this equation?

Tip:

In linear Diophantine equations, if gcd(a,b)=d\gcd(a, b) = d, solutions exist only if dd divides cc. Always use the Extended Euclidean Algorithm for such problems.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Number Theory
Linear Diophantine Equations
Extended Euclidean Algorithm

Formulas

gcd(a, b) = d
a = bq + r (Euclidean Algorithm)
ax + by = gcd(a, b)

Theorems

Euclidean Algorithm
Extended Euclidean Algorithm

Suitable Grade Level

Grades 9-12