Because what happened to this negative right over here? So it would have made sense for her to do the derivative of seven, and she could have said minus the derivative of five x. That's one possibility that she could have done. The derivative of a difference is equal to the difference of the derivatives. We've seen that property. Or she could have said the derivative, she could have said this is equal to the derivative of seven plus the derivative with respect to x of negative five x. These two things would have been equivalent to this one.