hi Deon588

d(BA)/dx is a special notation used in the differential calculus.

It gives you a way of finding the maximum value of an expression (amongst many, many uses!).

It's too big a topic to start in answer to the question, if you haven't met it before.

But don't worry. As the expression

is a quadratic there's another way to get the maximum value.

I've put the graph below. As you can see it does have a maximum value. Would you be able to work out the x, at this point?

Bob