and
if we eliminate phi2
we let 
and because 
so we can slove 
above all ,we can slove in paper ,but how can we slove in mathcad?
above all ,we can slove in paper ,but how can we slove in mathcad?
not that easy because mathcad is not so clever as we are.
In fact, symbolics never was the strong side of Mathcad.
And then you have to keep in mind that Mathcads symbolics usually considers more cases than we usually do. Ver often we use assumptions we are not really aware of. For example that variables are real, not complex, that some variables will be positive, that a function would be unique (while considering all cases it is not), etc. Especially trig functions and logarithms can be very tricky with this respect. So Mathcad would try to consider all cases possible and therefore often does not arrive at the simple solution we have in mind. Mathcad does not give us many way to manipulate the outcome of a sole or simplification and simetimes rewrite and especially assume do not work correct and Mathcad would ignore it.
But if you have a specific way to solve a task in mind, odten you can at least let Mathcad help you a bit with the boring routine manipulations.
See attached a manual elimination of phi2 to solve for phi3. I know its dissappointing that Mathcad can't do it on its own, though. But then, maybe someone comes up with a clever combination of sunstitutes, assumes, rewrites which do the trick.
Valery Ochkov wrote:
We can do it without complex number
Sure, but I know that the way of representing it with complex numbers is very common in mechanics and kinematics literature, as is the series of elimination steps which lee sketched.
Nevertheless I hadn't recognized the formulas and thought they were parts of some kind of coordinate transformations ;-).
See for example the picture 5 (and others) here - http://twt.mpei.ac.ru/ochkov/Mathcad-15/kinematic.html
Think we would have to see the worksheets to judge which approach would be more suitable (and for what purpose?).
Its a big difference if you are after a closed, general and exaxt analytical solution as it was aked for here of if you are happy with a numeric one for specific values as I had presented it in my first reply and as you do in your animation sheets.
Of course I think that for most practical purposes a numeric solution will be sufficent, but its not for us to criticize (which you hadn't done, I know) someone looking for a symbolic one.
But finally Alan had succes and provided a way to let Mathcad find a symbolic solution. The honour of Mathcad is restored - thanks Alan! 
lee0714 李 wrote:
thank you for disscussing though I don not know the Russian
Ai du not nou Inglish tuu bat Ai nou Guugle translator
PS
When I was in China (with topics on Mathcad), I used a taxi so. I showed to a taxi driver (he had not spoken English) on the city map, where do I go, and taxi driver showed me on the speedometer, how much it will cost in yuan. And we fine understood each other! 
