It seems like you'll need two numbers that differ by 100, which we'll call X and X-100. You want the minimum product of these two numbers, which means you'll want the derivative of the function X * (X - 100).
NOte that X * (X - 100) = X^2 - 100X, which is easier to differentiate. It results in a derivative of 2X - 100.
To find the mminimum, set this equation equal to 0, and you'll get
2X - 100 = 0 ===> X = 50. So your two numbers would be 50 and -50, with a minimum product of 50 * -50 = -2,500.
- Steve J