I am struggling with a Linear Algebra problem that involves finding the length of a 3-dimensional vector $\mathbf r$, as shown in the picture I sketched:
I do not have the coordinates of the points in this case, but for example, I know that the length of the vector $\mathbf v$ is:
$$||\mathbf v||=\sqrt{x^2+y^2+z^2}$$
Is there any similar way to find the length (in respect to $x$, $y$ and $z$) of the vector $\mathbf r$ in this case? If so, could anyone please explain me?