What justifies the t-1; to achieve this result?

restart;
interface(warnlevel = 0, imaginaryunit = I, rtablesize = 12);
with(plots); with(plottools);
alias(FFT = DiscreteTransforms[FourierTransform], IFFT = DiscreteTransforms[InverseFourierTransform]);

Temp := [24.2, 28.4, 32.7, 39.7, 47.0, 53.0, 56.0, 55.0, 49.4, 42.2, 32.0, 27.1];
POI := seq([n, Temp[n]], n = 1 .. 12);

 p1 := pointplot([POI], labels = ["x~month", "y = Temperature~ºF"...

why the command does not work: _EnvHorizontalName := x;_EnvVerticalName := y?

And a few lines later asks me the name of the axes

restart;
with(plots); with(plottools);

The circle S with center at the origin and radius 2 is given by the equation x2 + y2 = 4
The circle S have two tangents passing through the point (4, 1). Find the equation for each of them.
x^2+y^2 = 4;

subs(y(x) = y, solve(diff(subs(y = y(x), x^2+y^2 = 4), x), diff(y(x), x)));

I can not get any subscription in the forum for any topic. Activating the subscription link directs me to the page:

http://www.mapleprimes.com/controls/#


Without the subscription validity.

How can I use the command outputs DEtools [convertsys] for solving the system of differential equations? I know that maple can solve the system directly. But most of the examples can be seen in other systems (MathCad, MatLab ..) reduce the system to a system of first order equations. And I would like to implement, "translate" into Maple in this way. Is there a command that allows it? Do I need to implement a procedure?

GRACIAS

Using Maple for Functions of a Random Variable

How to make a query is made to F (t) at each iteration of the dsolve command?...

restart;
de:=m*diff(x(t),t$2)+b(t)*diff(x(t),t)+k*x(t)=F(t);                 
a random force :
nd := Statistics:-Sample(Uniform(-100, 100)):
F:=proc(t) ;   
if not type(evalf(t),'numeric') then