Solution for Section 3.9 Question 1

1. First apply the Euclidean Algorithm to 221 and 91 to find gcd(221, 91).

221

=

91 · 2 + 39     (equation 1)
91 = 39 · 2 + 13 (equation 2)
39 = 13 · 3 + 0 (equation 3)

Thus, gcd(221, 91) = 13. Since 13 | 676, we know that a solution exists to the linear Diophantine equation 91x + 221y = 676.

Now work backwards through the equations of the Euclidean Algorithm to find a solution.

From equation 2 we see that:

13 = 91 - 39 · 2
= 91 - [221 - 91 · 2] · 2 (from equation 1)
= 91 · 5 - 221 · 2

Therefore,     91(5) + 221(-2) = 13.          So we multiply both sides of the equation by 52 to get:      91(260) + 221(-104) = 676.

Hence x = 260 and y = -104 is one solution to the linear Diophantine equation 91x + 221y = 676.

Back to Section 3.9