I want to make sense of the expression

Int(t^2/ln(t)*exp(-t), t=0..infinity);

The denominator vanishes at t=1.  The singularity at t=1 is not integrable.  I want to see whether the integral is defined in the sense of Cauchy principal value.  Thus, I let

K := Int(t^2/ln(t)*exp(-t), t=0..1-a) + Int(t^2/ln(t)*exp(-t), t=1+a..infinity);

and wish to see whether the following limit exists:

limit(K, a=0, right);

Maple cannot evaluate this.  Nor can I.  Alternatively, we may try:

series(K, a=0);

or

series(K, a=0) assuming a>0, a<1;

In both cases Maple says that it is unable to compute the series.

So my question is: Does the Cauchy principal value exist, and can Maple help one to determine that?

I have the following equation

phi = -arctan(sin(2*theta)*(cos(beta)-1)/(cos(beta)*cos(2*theta)-cos(2*theta)-cos(beta)-1))+theta;

In the denominator I wish to collect the two cos(2*theta) terms  into a single term, as in

Is there a straighforward way of doing it?

i recall having asked this question before and having received answers which unfortunately I cannot locate.

I wish to generate a sequence like
    a[1], b[1], a[2], b[2], a[3], b[3]

The following does not work for the obvious reason:

    seq(a[i], b[i], i=1..3);

What is the right way?

The equation tan(y) = 2*tan(x) defines y implicitly as a function of x.  Well, perphas "defines" is too strong a word, since there are multiple solutions for y.  However, if I am not mistaken, there exists a unique continuous solution y(x) that goes through the origin, that is, y(0)=0, and is defined for all x.

Question 1: How do we plot the graph of y(x)?

I have a roundabout solution as follows.  Differentiate the equation tan(y(x)) = 2*tan(x) with respect to x and arrive at a first order differential equation in y(x).  Solve the differential equation with the initial condition y(0)=0.  Surprisingly, Maple obtains an explicit solution:

which we can plot:

plot(rhs(%), x=0..2*Pi);

Question 2: Is there a neat way of getting that solution with algebra only, without appealing to differential equations?