Take the tour ×  I have an electron in a 3D space and there is a
uniform constant magnetic field $B$, oriented according to
z-axes.  At $t=0$, we have $z=0$ and $\dot z =0$.  I have proved
that the trajectory is a circumference and that the motion is
uniform. Now I have to find the center of the circumference.  I
have found the radius:   And I have thought that I could find
the coordinates of the center considering:  $$R_x= \frac{m \dot
x}{qB} \rightarrow x-x_c=\frac{m \dot x}{qB} $$  $$R_y= \frac{m
\dot y}{qB} \rightarrow y-y_c=\frac{m \dot y}{qB} $$  Is it
correct?  share|improve this question Why don't you just define
that the x=0 and y=0 are the origin of R? –  anna v Feb 8 at
19:15 @annav It could be a good idea, but let's suppose that I
can't do it.. ;) –  sunrise Feb 8 at 20:05 Then you are solving
a simple geometrical question, "given a point at x_c and y_c on
the periphery of the circle with radius R where is the center in
cartesian coordianates?". No need of differential equations. The
charged part