Constant K

I think we can go without the constant K. It's simply 1 energy unit and 2 energy units. Also, when taking the derivative of E(x), I think it would be nicer to include the factors (2)(2x)(1/2) instead of simply 2x.

I will be honest I don't like it without the constant. I think we should be trying to encourage students to do some slightly abstract mathematics.

However I changed it based on this suggestion.