Write so:

A:= Matrix(2,2,[-5,2,-3,4]):

B[1] := [1, 1];

A[op(B[1])];

plot3d(x^2+y^2, x = -1 .. 1, y = -sqrt(1-x^2) .. sqrt(1-x^2), style=surfacecontour, contours = 4);

If you wish to withdraw from the assignment of A and B and fully return to the symbolic variables A and B, we can write:

A:='A':  B:='B':

 A;  B;

    A

    B

If you want to use the A or B as symbol variables to refer to, you can write:

'A'=A; 'B'=B;

Usually, Maple does not solve completely these rather complicated non-linear equations, therewith containing a parameter (in your equation, n - parameter). The reason apparently is that Maple can not compute the integrals for any values ​​of the parameter. The problem can be solved if  to specify value of the parameter.

Example:

Eq:=((diff(R(r), r, r, r, r))*r^4+3*(diff(R(r), r))*r-3*(diff(R(r), r, r))*r^2+2*(diff(R(r), r, r, r))*r^3-3*R(r)+4*R(r)*n+2*R(r)*n^2-4*(diff(R(r), r))*r*n+2*(diff(R(r), r))*r*n^2+4*(diff(R(r), r, r))*r^2*n-2*(diff(R(r), r, r))*r^2*n^2-4*R(r)*n^3+R(r)*n^4)/r^4 = (-108-1362*n+2122*n^2+2019*n^3-3032*n^4+401*n^7+1192*n^6-1033*n^5-25*n^9+6*n^10-180*n^8-4128*r^(n+3)*n^3+2304*r^(n+3)*n-576*r^(n+5)*n-760*n^6*r+575*n^5*r-244*n^7*r-2108*n^3*r-11616*r^(n+3)*n^4-5280*r^(n+3)*n^5-456*n^2*r-6912*r^(3*n+3)*n^3+192*r^(n+3)*n^7-6*n^10*r+152*n^8*r+13*n^9*r-192*r^(n+5)*n^7+4224*r^(3*n+3)*n^2-9216*r^(3*n+3)*n^5-16512*r^(3*n+3)*n^4-1632*r^(n+5)*n^6-1536*r^(3*n+3)*n^6-7680*r^(n+5)*n^3-8832*r^(n+5)*n^4-3360*r^(n+5)*n^2-96*r^(n+3)*n^6+2304*r^(3*n+3)*n-5376*r^(n+5)*n^5+2546*n^4*r+4800*r^(n+3)*n^2)/(576*r^4+192*r^4*n^4+1248*r^4*n^3+2688*r^4*n^2+2208*r^4*n):

n:=2: dsolve(Eq, R(r));

algsubs(cos(t)/sin(t)=cot(t), cos(t)*cos(u)/sin(t) - cos(t)^2*cos(u)/sin(t)^2);

Try so:

normal(convert(sin(t)/(1+cos(t)), tan));

After with(geometry):  write assume(a,real): 

Maple does not know that you suspect this condition!

Code of procedure:

P := proc (Eq)

local z, u;

z:=rhs(Eq)^(1/op(2,lhs(Eq)));

u := evalc(z);

if is(0 <= Re(u)) and is(0 <= Im(u)) then abs(z)*(cos(argument(u))+I*sin(argument(u))) else abs(z)*(cos(argument(u)+2*Pi*op(2, z))+I*sin(argument(u)+2*Pi*op(2, z)));

end if;

end proc;

Example:

P(w^11=-5-5*I);

palindrome:=proc(n)

   option cache;

   uses ST = StringTools;

   if 

    modp(length(n),11)<>0 then

   return false;

   else

   return ST :- IsPalindrome(convert(n,'string'));

   end if;

end proc;

Use the seq command.

Example:

A:=seq(Vector([-2+3*i, -1+3*i, 3*i]), i=1..10):

ArrayTools:-Concatenate(2, A);

Here is a variant which suitable and for older versions of Maple (with only Classic Worksheet):

A:=plot([exp(-x),x^2], x=-0.5..1.5,color=black,thickness=2):

h:=fsolve(exp(-x)=x^2):

B:=plot(x^2,x=0..h,color=white,filled=true):

C:=plot(exp(-x),x=0..h,color=red,filled=true):

E:=plot([0, t, t=0..1], color=black, thickness=2):

plots[display](A,B,C,E,scaling=constrained,view=-0.3..1.7,labels=["x","y"]);

Yes, of course!

Example:

And what's the problem? Symbolically your system is solved correctly. This system can't be solved numerically, since it contains three parameters: v, va, f (t) .

Your function y(x)=-2*x^2+C1*ln(x)  is the solution of a differential equation

x*ln(x)*diff(y(x),x)-y(x)=2*x^2-4*x^2*ln(x)  which has no solutions for x<=0, since the domain of the function ln (x) only positive numbers.