inverse geometrice model robot

Hi,

i'm studying a robot arm

i have done davenit and direct geometric model and i obtain this equations system

J'ai essayé par des substitutions du type cos=1-u²/1+u² mais le système devient rapidement inextricable....
system

eq1=335*cos(t2)* sin(t3) -77*sin(t2)-260*sin(t2)*sin(t4)+260*cos(t2)*cos(t3)*cos(t4)+85=x;
eq2=335*cos(t3)-260* sin(t3)*cos(t4)=y;
eq3=0-335*sin(t2)* sin(t3) -77*cos(t2) -260*cos(t2)*sin(t4)-260*sin(t2)*cos(t3)*cos(t4) =z;
which is equal to

(1)S+(2)*C2 =>eq1=260*sin(2*t2)*sin(t4)== 8-x*sin(t2)-z*cos(t2);
eq2=335*cos(t3)-260*sin(t3)*cos(t4)-y==0;
eq3=0-335*sin(t2)* sin(t3) -77*cos(t2) -260*cos(t2)*sin(t4)-260*sin(t2)*cos(t3)*cos(t4) =z;

avec T2 [ -PI/4. PI/2] T3[ -PI/4 PI/4] T4 [0 PI/2 ]

Now i want to solve it and express t2 = f(x,y,z) t3=g(x,y,z) t4 = h(x,y,z)

it ty many ways (paul method susbstitution cos=1-u²/1+u²) but i don't manage to find the results

If someone can help me even with a computing solution fro mapple and so on

thanks