Hi all ---

I understand the circle equations. And I understand the vector joining the two centers of the circles is just ---

$\displaystyle [1,1] - [5, 4] = [-4, -3]$ so its norm is $\displaystyle \sqrt{(-4)^2 + (-3)^2}$

But I don't understand the $\displaystyle \frac{2}{5}(-4, -3)$ in the last line at all. Where does it come from? What does it mean?

Thanks a lot ---