I am stumped with this trivial puzzle.  Let
z := arctan(x/sqrt(a^2-x^2));
                    
How do we simplify z to.

I tried all sorts of tricks with simplify(...) and convert(...), with assumptions, but did not get anywhere.  Any clues?

Versions: Maple 2016 and 2017.

Let A and B be regions in space defined through f(x,y,z) > 0 and g(x,y,z) > 0, respectively.  How does one plot the surface of the object A ∩ B in Maple?

In Mathematica there is a command RegionPlot3D for that.  See sample here.  Perhaps there is an equivalent one in Maple that I don't know of.

Consider a standard initial/boundary value problem for the heat equation on the interval x ∈ [0,1]:

restart;
pde := diff(u(x,t),t) = diff(u(x,t),x,x);
ic := u(x,0) = f(x);
bc := u(0,t)=0,  u(1,t)=0;

Then
pdsolve({pde, ic, bc});
produces the expected Fourier series solution.

However, if we change the interval to x ∈ [-1,1], as in:
bc := u(-1,t)=0,  u(1,t)=0;
pdsolve({pde, ic, bc});
then Maple fails to return a solution.  Why?

It is evident that by repeated applications of the double-angle and product trigonometric identities, one may transform any monomial of the form sin(x)^p * cos(y)^q, where p and q are positive integers, to a linear combination of only first powers of sines and cosines.

Example 1:  The monomial  4*sin(x)*cos(y)^2 is equivalent to

Example 2: The monomial 16*sin(x)^2*cos(y)^3 is equivalent to             

How does one write a Maple procedure to do that transformation in the general case of sin(x)^p * cos(y)^q?

Let

z := Diff(x(t),t)*y(t) + x(t)*Diff(y(t),t);

Is there a way to tell Maple to collapse that into Diff(x(t)*y(t), t) ?

I tried factor, combine, simplify, but none of them worked.