# problem with solve

i have problem with command solve ..it doesnt give any result even not a problem its just makes matlab busy and does nothing for hours .i give the code
:

syms th1 th2 th3 th4 px py pz eks d5 a3 a2

[ th1 th2 th3 th4] = solve( 'px=cos(th1)*(d5*sin(th4)*cos(th2)*cos(th3)-d5*sin(th4)*sin(th2)*sin(th3)+d5*cos(th4)*cos(th2)*sin(th3)+d5*cos(th4)*sin(th2)*cos(th3)+cos(th2)*a3*cos(th3)-sin(th2)*a3*sin(th3)+a2*cos(th2))' , 'py=sin(th1)*(d5*sin(th4)*cos(th2)*cos(th3)-d5*sin(th4)*sin(th2)*sin(th3)+d5*cos(th4)*cos(th2)*sin(th3)+d5*cos(th4)*sin(th2)*cos(th3)+cos(th2)*a3*cos(th3)-sin(th2)*a3*sin(th3)+a2*cos(th2))' , 'pz= d5*sin(th4)*sin(th2)*cos(th3)+d5*sin(th4)*cos(th2)*sin(th3)+d5*cos(th4)*sin(th2)*sin(th3)-d5*cos(th4)*cos(th2)*cos(th3)+sin(th2)*a3*cos(th3)+cos(th2)*a3*sin(th3)+a2*sin(th2)','257/2000*((cos(th1)*cos(th2)*cos(th3)-cos(th1)*sin(th2)*sin(th3))*sin(th4)-(-cos(th1)*cos(th2)*sin(th3)-cos(th1)*sin(th2)*cos(th3))*cos(th4))*d5-1019/2500*((sin(th1)*cos(th2)*cos(th3)-sin(th1)*sin(th2)*sin(th3))*sin(th4)-(-sin(th1)*cos(th2)*sin(th3)-sin(th1)*sin(th2)*cos(th3))*cos(th4))*d5=0', 'th1' , 'th2', 'th3','th4' )

pls help me ..its urgent please