@Markiyan Hirnyk  I usually work in the classic interface and have never met such problems. In this situation in the code of the procedure it is necessary to replace  $ i  to  `$`(i)

@Markiyan Hirnyk  Unfortunately, your code returns unevaluated the same example:

restart; m := 3;

f :=  (x,y,z)-> 1/x/y/z:

rang[1] := 1 .. 5; rang[2] := 2 .. 8; rang[3] := 3 .. 7;

VectorCalculus:-int(f(seq(floor(k[i]), i = 1 .. m)), [seq(k[i], i = 1 .. m)] = Parallelepiped(seq(op(1, rang[j]) .. op(2, rang[j])+1, j = 1 .. m)));

@Carl Love  Of course, your method using viewpoint option witty and programmatically solves the problem but:

1) Zooming by the mouse is the simplest and fastest way to get the same effect

2) In the second method  we have actually  a uniform  stretching of the plot along axes and effect is the same, excepting the simultaneous stretching of tickmarks.

I think Carl's solution by simplify/siderals is the most simple and natural way.

Thank you all  for your answers!
If we replace the assigning by an usual substitution, the results remain identical. What's the difference?

restart;

V1:=Vector([a, b]);  V2:=<a, b>;  # Identical results

A:=subs({a=[1, 2],b=[3, 4]}, V1); B:=subs({a=[1, 2],b=[3, 4]}, V2); # Also identical results

whattype(A); whattype(B);

Since 1/1 = 1, then why just  1  not written?

Maybe should be  1/(1-exp(a*x))*erfc(a*x)  or  1/((1-exp(a*x))*erfc(a*x))  ?

@Alejandro Jakubi  Your way does not work if in solutions there is no the number  Pi . Here is more general way:

s := solve({x >= 0, 2*sin(Pi*x) = 1, x <= 2*Pi}, AllSolutions, Explicit);

seq({x = convert(rhs(op(s[i])), degrees)}, i = 1 .. nops([%]));

@acer 

At first I wrote  Diff  and Maple showed all the steps, then I replaced  Diff  by  diff  and Maple again showed all the steps. But if from the beginning written  diff, the error appears.

@oldstudent 

Maple 16

@Markiyan Hirnyk 

Thanks for the comment. Indication of editing done.

@oldstudent 

with(Student[Calculus1]):

A := diff(x^2*sin(x), x);

ShowSolution(A);

Another way to solve the problem, first create a matrix of the correct size, and then make the necessary substitutions or conversions.

x := [i $ i=1..25];

A:=Matrix(5, x);

eval(A, [seq(x[i]=convert(x[i], string), i=1..nops(x))]);

@bluehotel  Just copy the bold text below into Mathematica and press the key Enter:

Reduce [{-x3 * x5 /m - x3 * x5 - 2 * x1 * x5 + 2 * x1 == 0, 
x3 * x5 /m - 2 * x2 * x5 + 2 * x2 == 
0,-х3 + 2 * x5 - x3 * x5 + 1 - 3 * x1 - 3 * x2 + x4 == 
0, -2 * x4 - 2 * x4 * x5 == 0,-x3 * x5 ^ 2 / (x1 * m) - 4 * х5 ^ 2 + 4 * x5 == 
0}, {x1, x2, x3, x4, x5}] // TraditionalForm

@liumai   rhs((P(k))(t)[2])  is the right side of the second operand of the list  (P(k))(t)  for specific  k  and  t .

For 2 functions in the system replace  (k, t)->rhs((P(k))(t)[2])  by the list  [(k, t)->rhs((P(k))(t)[2]),(k, t)->rhs((P(k))(t)[4])]

@Carl Love  Your code in M 12 also works. I think  evala  command is crucial. I used  expand  command instead  and got the message "lost connection with the kernel"