Two numbers have a difference of 28. What is the sum of their squares if it is a minimum?

Now the square of x is x^2 and the square of x + 28 is (x+28) ^2.

The sum of the squares is x^2 + (x + 28) ^2.

x^2 + (x + 28) ^2

= x^2 + x^2 + 28^2 + 56x

= 2x^2 + 28^2 + 56x

Now let f (x) = 2x^2 + 28^2 + 56x