why can't i solve this non-linear equation group

[happybird]

i try to use the"Non-linear system solver.Vi to solve a four variable equation group like the following:
0.5*(5.70931+d)+0.5*sqrt((5.70931-d)**2+4*b**2)-5.92931=0;
0.5*(5.70931+d)- 0.5*sqrt((5.70931-d)**2+4*b**2)-5.85613;
0.5*(5.70931+a)+0.5*sqrt((a-5.70931)**2+4*b**2)-9.51533;
0.25*(a-2*b+2*5.70931+10.459)+0.25*sqrt((2*b-a+10.459)**2+4*(c+5.70931-b)**2)-8.66606;
why i can not get the result? is that because it is too complex to be solve by LABVIEW7.0?
thanks!

[dongbin]

I can not also get rational roots of b and d only with the first two equations with Matlab? pls check your equations.