離散1-60 例題54

Note a = b ( mod n ) -> ma = mb ( mod n )

假設 gcd ( m , n ) = 1

ma = mb ( mod n ) -> a = b ( mod n )

請問

7 * (-104) = 13 (mod 19)

=> (-104) = 10 = x ( mod 19)

這是不是也要限定gcd ( 7 , 19 ) = 1