Example 5 Solve the congruence equation .
Solution
This is a linear congruence equation, which can of course be solved using the method in §2. Here, we transform it into a system of linear congruence equations with smaller moduli, which is sometimes more convenient. Since , by the property [X] in Chapter 3 §1, this congruence equation has the same solution as the system of congruence equations
Using the equivalent transformation I in §1, this system of congruence equations becomes
Furthermore, using the equivalent transformations III and I of 11 (i.e., solving the second, third, and fourth equations in the above system of congruence equations), the system of congruence equations becomes
This system of congruence equations can be solved using the method in Theorem 1. In fact, this is the system of congruence equations in our Example 1, and its solution is
This is the solution to the original congruence equation.