Maths Olympiad Prep

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Number theory Difficulty 5.0 AIME, harder Find the answer

Example 1 Find the number of positive integer solutions to the indeterminate equation
7x+19y=20127 x+19 y=2012

A number or a short expression. Spacing and $ signs are ignored.

Solution

Solve: First, find a particular solution of (1).
x=17(201219y)=2873y+17(3+2y).x=\frac{1}{7}(2012-19 y)=287-3 y+\frac{1}{7}(3+2 y) .

Therefore, 17(3+2y)\frac{1}{7}(3+2 y) must be an integer. Taking y0=2y_{0}=2, then x0=282x_{0}=282.
Using the conclusion of Theorem 2, the general solution of equation (1) is
{x=28219t,y=2+7t. ( t is an integer )\left\{\begin{array}{l} x=282-19 t, \\ y=2+7 t . \end{array} \text { ( } t \text { is an integer }\right)

Combining x>0,y>0x>0, y>0 and tt being an integer, we can solve to get 0t140 \leqslant t \leqslant 14.
Therefore, equation (1) has 15 sets of positive integer solutions.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.