Symbolic Math Toolbox:
syms L D
Eq1 = D^2* L == 51.8/(1087*25);
Eq2 = L/D == 1.178;
[Ls,Ds] = solve(Eq1,Eq2,[L,D]);
Lv = vpa(Ls)
Dv = vpa(Ds)
producing:
Lv =
- 0.06914916395087665 + 0.1197698652638286i
- 0.06914916395087665 - 0.1197698652638286i
0.1382983279017533
Dv =
- 0.0587004787358885 + 0.1016722115991754i
- 0.0587004787358885 - 0.1016722115991754i
0.117400957471777
There are other ways to solve them as well.