I’m am reading my textbook, but I’m having a hard time understanding how they got to the next step.
The text says to take a division problem and put it in the format of
b/a = b * a-1 mod m
And that the inverse a-1 of a number is defined such that
a a-1 = 1 mod m
Problem: what is 5/7 mod 9?
The explanation given in the text.
“The inverse of 7 mod 9 is 4 since 7*4= 28=1 mod 9”
I can’t figure out where the 4 comes from.
I used the equations from the above, but I don’t see how the 4 comes about.
( 7*7-1 = 1 mod 9 )= ( 1 = 1 mod 9) ?