Two Positive Numbers Have A Product Of 16. Find The Minimum Value Of Their Sum?

Let 1st number be: X
let 2nd number be: Y
let the minimum be: M

1   x-y=16 -->  x=16+y
2   m=x+y+xy

sub 1 into 2

m=(16+y)+y+(16+y)y
   =y^2+18y+16
y^2+18y+81-81+16
m=(y+9)^2-65
therefore y=-9

sub y=-9 into 1

x=16+(-9)
x=7

therefore the first number is 7 and the second is -9