Question 1042995
Since d is a factor of x, there exists a positive integer e
such that x = d*e .
Since d is a factor of y, there exists a positive integer f
such that y = d*f .
So x*y = (d*e)(d*f)
Since order is not important in multiplication
x*y = (d*d*e*f) or x*y = d^2*e*f
and d^2 is a factor of x*y