farz konid (a,b) = d . darim a = da` va b = db` ke (a`,b`) = 1. va tebghe farz darim (a,b,c) = (d,c) = 1
.(`hal tebghe sooorate soal darim ab = c(a-b) ==> d[SUP]2[/SUP] * a` * b` = d * c * (a`-b`) ==> d * a` * b` = c (a`-b
d | c(a` - b`) . chon (d,c) = 1 pas darim d | a` - b` . az tarafi chon ( (a`-b`), a`b`) = 1 pas darim a` - b` | d
.in natije midahad ke a` - b` = d . hal a - b = d ( a` - b`) = d[SUP]2[/SUP] . pas a - b moraba kamel ast .