# Math Help - differentiation: first principles

1. ## differentiation: first principles

http://i1163.photobucket.com/albums/...tprinciple.jpg
I can't follow the steps. How does the 2nd step go to the 3rd one?

Thanks a lot!

2. ## Re: differentiation: first principles

Each term in the numerator and denominator has been divided by the common factor $\Delta x$.