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The green box indicates that Mathcad is trying to calculate.

When trying to solve symbolically (as you show), I also get the green box while Mathcad tries to find the solution.  I did not wait long enough for it to finish.  You can try letting it run in the background to see if it ever finishes.

Do you need a symbolic solution, or would a numerical solution work?  When I try to solve numerically with d=0 as the guess value, I get an undefined error.  However, when I change the guess to 0.00001, I get the following:

Your sking for a symbolic solution, but with the powers of d that's not going to work.

Problem is numerically solvable, using the root function.

(If 'difficult expression'=m, then 'difficult expression' - m must be zero, that's what the root function will search.)

Now the result is complex, did you expect that?

Success!
Luc

Hi LucMeekes & Mark Gase,

Thanks for your reply ! I'm searching for a real solution, the value that i get should be the diameter of a critical orifice (for in-compressible flow).