The only force acting on a particle with charge e and velocity **v**, in a constant magnetic field **B**, is e**v** × **B**. Also, **r**(0)=0 and $\displaystyle \dot{\textbf{r}}(0)=\textbf{V}$.

I've shown that: $\displaystyle m\dot{\textbf{r}}=e\textbf{r} \times \textbf{B} + m\textbf{V}$.

Now the question asks to find equations for the path of the particle if **B**=(B,0,0) , **V**=(v_1,v_2,0) and **r**=(x,y,z).

I evaluated the cross product and equated the components to get:

$\displaystyle \dot{x}=v_1$

$\displaystyle \dot{y}=\frac{eB}{m}z + v_2$

$\displaystyle \dot{z}=\frac{eB}{m}y$

By solving the second and third equations, I generate equations involving exponentials but the answer has equations involving sin and cos.

Can someone see where I've gone wrong? Thanks in advance.