@vv it's going to work for sure. but i was waiting for maple to do it directly without needing to list a sequence and stuff like that, you know...and it seems strange to me that it worked for single integrals, but not for double ones. also expression even return an answer to me when im asking for an specific time, but plotting doesn't work.

@vv isn't there a way to do it directly with the expressions? I have done this before using simple (single) integration....it worked perfectly. Now i'm trying with double ones, i get nothing. Maybe a maple's bug?

@Kitonum this is not an space curve...the three x's are three different displacements, the only variable for each one there is t2. I have manually set t2 for the first expression to 1/3 sec and it gave me a solution. However, if try to plot the same for t2 from 0 to 1/3, doesn't return nothing. So i think it should be a way to plot double or triple integrals...

@tomleslie i could solve the problem at the end. i found another mistake: it was -4<=(4000 `Q`)/(Pi `D`^(2))<=4, a conversion mistake. SolveEquation command is just amazing, i downloaded the Direct search package from somewhere, and just found how to work with it. it looks pretty superior to fsolve, i think maple should update the fsolve command using this method (i have no idea which, either how it works). at the end i just assumed each one of D's and solved a 10x10 system for the Q's. it worked perfectly well. i could bet taking -4<=(4000 `Q`)/(Pi `D`^(2))<=4 as restrictions on SolveEquation had solved the matter too.aceitoso.mw

@Carl Love sorry about that, im just a "noob" using maple. In fact, i have not coursed any class about it, and im not a programmer either. Just a guy who thinks maple is awesome and learning by myself... so that's why i did it. But im going to try to remove output next time before posting, thanks.

@tomleslie last equations are not equations itself, they are rather restrictions, so i need velocity to be between 0 and 4. im not sure if there is a way to solve the problem with ecuations and inequalities on it, working with -4<= 4 Qi/pi Di^2 <=4. i uploaded a new file and wrote the inequalities or restrictions in the fsolve command, 10 equations and 10 inequalities... i also modified the Re numbers with an absolute value, although all solutions got before were positive, maybe there is a solution with a negative Q and maple cant find it because of the Re numbers being negative... thanks for your help aceitoso.mw
 

Download aceitoso.mw

@tomleslie i fail to put absolute value on last 10 equations, so i builded the system in such a way that a negative Q indicates wrong direction choice, so i coud have supposed any of this Qs wrongly. could you please show me wich command are you using to solve something like this in your answer please? i feel fsolve sometimes requires very close initial values to find a solution, and sometimes it just can't... i have uploaded the corrected file on this reply... thanks for your help aceitoso.mw
 

Download aceitoso.mw

@vv i would like to know that, i have no idea what an rhs is...

only think i know is how to extract the results from the list procedure i got. and there is not a second derivative for y(x) in that. it could be very usefull to know something like that..

thanks..

@ it looks like all you have to do is letting your system expressed like da/dt = "something", db/dt = "something",.... putting enough initial conditions, and if expression is not a big amount of polynomius, it could easily solve. It's not like that? 

@ 
 

only thing i did was differentiate my two last ecuations, and then i needed to insert two more initial conditions for T1 and T2. like you said before, system ask for T1s because there is another solution, if i'm not bad with T1s= - 60.364...

that was all i required, although the system continue identifying it like a DAE, but now i got a solution.  
 

Download solucion_ecuation_1.mw

@Carl Love 
 

by the way, it was a time memory didn´t change at all, neither time, maybe it entered in an infinite loop or something?
 

Download ecuation_1.mwecuation_1.mw

@Carl Love hello again,

I remembered what you said about that exponent on denominator and i replace it by a fifth grade polynomium using curve adjust. so i ran it again but i has been an hour and still no answer. why would be it taking so long? i have worked even with a double pendulum ecuation before, with very wide and long trigonometric expressions for theta, like sin() and cos(). however i could get an answer in less than a minute, just a few seconds of evaluating (something like 10 sec max).  

@Carl Love thank you very much, i had no idea a system like this could take so long. which is more, i didn't even know maple could keep evaluating an expression for days! that's crazy and amazing 😂. do you think an ordinary computer could resist so much time processing? it doesn't matter if my screen auto-black-out (some times when computer stays in recess so much time, screen just turn off saving energy), i mean, calculations are not interrupted? 

@Carl Love ecuation_1.mw
 

ok, thank you for answer me. here is my input in typed commands, i also have uploaded a couple days ago another corrected ecuation with the hole process in order to explain my problem, althought with some mistakes. i just uploaded the maple document right now, so you can open it and try to evaluate it by yourself. that's the DAE i can't solve. 

it would be great if could at least reply telling why maple just kept evaluating it and doesn´t give me a procedure. do i have to give a long while for calculations or something? thank you very much.

Download ecuation_1.mw

@tomleslie or you have no idea?...say something at least. it appears like maple can't solve EVERY ecuation can be solved. 

Waiting for your answer...