@janhardo It is difficult to learn Maple when the examples involve unknown maths methods.
To be efficient, I suggest to solve first those problems for which the maths is clear for you. After that, your Maple knowledge will be good enough to approch other problems. Keep in mind that when solving a math problem in Maple (for which a direct command does not exist)  you will have to know/read/review the existing methods (or maybe to invent or rediscover them!) .

@janhardo 

@Danial If you are interested in the exact solution, you could rewrite (by hand) the inequality as a system of polynomial inequalities and then call solve or SemiAlgebraic. Unfortunalely Maple is not able to do this automatically.

P.S. In general it is is not possible to visualize inequalities in 3D. Try e.g. 
(x^2+y^2+z^2-1)*(x^2+y^2+z^2-2)<=0.
 

@rameen hamood 

It is easy to write it by hand (which I suppose you should do). Or, execute

LinearAlgebra:-GenerateMatrix([x1+6*x2, -2*x2, -4*x1+2*x2], [x1,x2]);

and select the matrix.
 

@nm You are confusing the OP.  A is a 5x4 matrix, so A.x makes sense and is the column Vector: 
<2298, -531, -160, -503, 579>
 

@nm Your initial ode is 
(2*x+y)/(3-x+3*y^2) dx - dy = 0; # M = (2*x+y)/(3-x+3*y^2), N = -1

It is not exact.

@michalkvasnicka 

For a more robust approach see Acer's answer. But you should be aware than any CAS may fail to solve directly your problem. If you know the maths behind it and the CAS language you have big chances to get a result. If not, it remains to complain about it.

@Fancypants The points are not unique, you are missing a condition.
It's not difficult to give an example, e.g. all Lij equal to 1 or 2.

@Fancypants Initially, all Lij were known. Now you say that some are not known. It's not the same thing!
In your picture, P0, P2, P3 seem to be collinear. If true, the number of needed Lij known could be decreased by 1. In principle this number must be >= 10 for a unique solution, but not any 10 will guarantee the uniqueness. Anyway, in this case a symbolic solution is improbable. If your problem is numeric you have the possibility to use DirectSearch to solve the system.

@michalkvasnicka 

If you try to solve f = 0, where

f := x^2 + 2*x + floor(x^2 + x)-25;

Mathematica answers:  This system cannot be solved with the methods available to Solve.

In Maple do (using the presented method):

seq(solve({eval(f,[floor(x^2 + x)=n]), n<=x^2 + x, x^2 + x<n+1}), n=-1..20);

      {x = -1 + sqrt(15)}

@Carl Love

Yes, thank you. Actually I have an enhanced version. It was written immediatley after the module version, but I forgot to replace it. I did it now.

@vs140580  I don't understand what you are trying to obtain. After relabelling the graph looks as in your picyure. I use GraphTheory for computations, not for drawings.
 

@Kitonum It must be noted that identify usually must be used with higher precision and works only for very simple results.
E.g. for eq := x^2+floor(x)-3*Pi  it fails.
 

@Carl Love   Agree but without brackets.

@DarkMath 

Maple does not document when Dirac(f(x))  is defined; Maple accepts f(x)=x^2-1  but rejects f(x)=x^4-1. It works formally, that's why the user must be careful. The usual conditions (f smooth and f' <> 0 at the roots of f) could be difficult to verify.