Solve function not working - matlab

Question

I'm currently trying to solve an equation with the solve function but I keep getting errors.
This is my code:
Dh=0.02;
Lc1=1.6;
Prw=9;
a=0.03*(Dh/Lc1)*Prw;
b=0.016*(Dh/Lc1)^(2/3)*Prw^(2/3);
c=9;
d=7.54;
syms Redh
eqn = (c*b-d*b)*Redh^(2/3)-a*Redh == d-c;
solRedh = solve(eqn,Redh);
When i run this i get the error
Warning: The solutions are
parameterized by the symbols: z2.
To include parameters and conditions
in the solution, specify the
'ReturnConditions' option.
In solve>warnIfParams (line 500)
In solve (line 356)
In Massflow_1 (line 105)
Warning: The solutions are valid under
the following conditions: 3*z2^2 + z2^3
- 59/50 == 0 & -pi/3 < angle(z2) &
angle(z2) <= pi/3.
To include parameters and conditions
in the solution, specify the
'ReturnConditions' option.
In solve>warnIfParams (line 507)
In solve (line 356)
In Massflow_1 (line 105)
I don't understand why the answer is parameterized by the symbol z2. There should be a solution containing a value. Even if i simplify it to an equation with the same powers of which I'm certain there is an answer to I get the same error.
Simpeler code
syms Redh
eqn = 0.0054*Redh^(2/3)-0.0034*Redh == -1.46;
solRedh = solve(eqn,Redh);
Does anybody know what is going wrong here and how I can fix it? It would be very helpful, thank you!

Answer 1

In your case, matlab use the symbol 'z2' to show that the solution use a complex number.(z2 ∈ Z)
You need to explain to matlab that you are not interested by a complex solution.
It should work without problem with:
% set an assumptions on symbolic variables! here our solution need to be a real number.
syms Redh real %check the doc for more informations about the assumptions.
eqn = 0.0054*Redh^(2/3)-0.0034*Redh == -1.46;
sol_sym = solve(eqn,Redh);
sol_nosym = double(sol_sym);