If the difference of two positive numbers is 3, find the least possible value of their product
Set up the equation for this: given a first number x and a second number x-3, their product is P=x(x-3). Determine dP/dx, set it to 0, and solve for x. This will give you either a minimum value for P or a maximum. So try it - what do you get for x? Is it a min or a max?