two trig. equations with two unknowns

hallo,

i need help solving these equations. i hope i'm posting in the right place.

these two equations are the first step in an iterative procedure. $\displaystyle \psi_0$ and $\displaystyle \beta_1$ are known and i need to find $\displaystyle \theta$ and $\displaystyle \beta_2$. the two equations are

$\displaystyle

\sin(\psi_0 - \beta_1 + \theta) - \sin(\psi_0 - \beta_1 - \beta_2 + \theta) - \cos(\psi_0) \sin(2 \theta) = 0

$

and

$\displaystyle

\cos(\psi_0 - \beta_1 - \beta_2 + \theta) - \cos(\psi_0 - \beta_1 + \theta) - \cos(\psi_0) \cos(2 \theta) - cos(\psi_0 - \beta_1 - \beta_2) = 0

$

the paper this is from says they used Newton-Raphson, which i could probably do if there was only one equation with one unknown, but with two equations i can't see how to procede.

if someone can help me out i promise i'll try and help someone else on here if i can!

cheers,

jack.