I have 2 equations that are made up of various powers of 2 different variables. Is there any command to retain only terms of the first order? E.g. no "x^2", "x^{3/2}", etc, just "x"s.

I want to solve a series of differential equations, and then plot the results, but I'm having a bit of trouble with evaluating them using dsolve. My code is:

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restart;

c:=1;
mu:=0.3;
m1:=1-mu;
m2:=mu;
x1:=mu;
x2:=mu-1;
omega1:=1/2(mu(1-mu)-3);
omega:=1+omega1/c^2;
r1:=sqrt((x(t)-x1)^2+y(t)^2);
r2:=sqrt((x(t)-x2)^2+y(t)^2);
A:=diff(y(t),t)*x(t)-diff(x(t),t)*y(t);
rsquared:=x(t)^2+y(t)^2;

You would have thought I'd have learnt to make sure I've saved my work by now.

I've spent the last 4 hours or so working on a worksheet on Maple, without saving it once (I know, I know). It started acting slow-- by which I mean it was talking a while to actually type things, as opposed to running calculations-- and then the screen suddenly went grey, froze, and now my cursor turns into an hourglass when I mouseover the window.

It's been this way for the past 10 minutes.

I'm having a few problems with differentiating in Maple. I have a potential function U given by:

U[c] := (1/2)*r^2+M[1]/r[1]+M[2]/r[2];

U[r] := r^2*(M[1]*M[2]-3)/(2*c^2)+((x(tau)+diff(y(tau), tau))^2+(y(tau)-(diff(x(tau), tau)))^2)^2/(8*c^2)+3*(M[1]/r[1]+M[2]/r[2])*((x(tau)+diff(y(tau), tau))^2+(y(tau)-(diff(x(tau), tau)))^2)/(2*c^2)-(M[1]/r[1]+M[2]/r[2])^2/(2*c^2)-M[1]*M[2]*(1/r[1]+(1/r[1]-1/r[2])*(1-3*mu-7*x(tau)-8*(diff(y(tau), tau)))+y(tau)^2*(M[2]/r[1]^3+M[1]/r[2]^3))/(2*c^2);

I'm trying to use dsolve to get a numeric solution to a series of differential equations I have. I've got:

G := 1;

M := 1;

pT := 2;

OrbitEnergy :=  (r0) -> -1/r0+(1/2)*L^2/r0^2-L^2/r0^3;

OrbitDEs := diff(r(tau), [tau$2]) = -G*M/r(tau)^2+L^2/r(tau)^3-3*G*M*L^2/r(tau)^4, diff(phi(tau), tau) = L/r(tau)^2, diff(t(tau), tau) = sqrt(r(tau)/(r(tau)-2*G*M)+(diff(r(tau), tau))^2*r(tau)^2/(r(tau)-2*G*M)^2+r(tau)^3*(diff(phi(tau), tau))^2/(r(tau)-2*G*M));