Four equations in four unknowns

diff((2), y);

diff((3), y);

diff((5), x);

diff((6), x);

diff((8), x);

diff((9), y);

-(1/16)*Pi^2*sin((1/4)*Pi*x)*(c__1*cosh((1/4)*Pi*y)+c__3*y*cosh((1/4)*Pi/y)+c__4*y*sinh((1/4)*Pi*y))=0;

eval( (12), [x = 0]);

eval( (14), [x = 20]);

eval( (16), [y = 9]);

evalf[5]( (17) );

eval( (19), [y = -9]);

evalf[5]( (20) );

eval( (22), [y = 9]);

evalf[5]( (23) );

eval( (25), [y = -9]);

evalf[5]( (26) );

s:=solve({sin(.78540*x)*(362.25*c__1+0.84938e-3*c__3+4182.6*c__4) = 0,sin(.78540*x)*(362.25*c__1-0.84938e-3*c__3+4182.6*c__4) = -1.*sin(.25000*Pi*x),-.78540*cos(.78540*x)*(461.22*c__1+.99617*c__3+4738.2*c__4) = 0,-.78540*cos(.78540*x)*(-461.22*c__1+.99617*c__3-4738.2*c__4) = 0},{c1,c2,c3,c4});