Help Solving an Equation

Hi,

I am trying to solve the following function for x where er, Re and d_i are known values:

x+4*log10(er/(3.7*d_i)+1.4125*x/Re)=0

I have tried several methods and cant seem to get the right answer. I know that the correct answer is approximately 10.8. Can anyone help me set this up?

Thanks in advance

Answer 1

[Star Strider]

You have to provide the correct values for the constants.

This will provide you with the numeric result:

syms d_i er Re x 
d_i = sym(3);                                                   % Insert Correct Values
er = sym(5);                                                    % Insert Correct Values
Re = sym(1000);                                                 % Insert Correct Values
Eq = x+4*log10(er/(3.7*d_i)+1.4125*x/Re) == 0;
x_sol = solve(Eq, x, 'IgnoreAnalyticConstraints',1);
x_val = double(x_sol)                                           % Desired Numeric Result

EDIT — You could do this numerically with fzero if you know the approximate value of the desired root:

d_i = 3;                                                        % Insert Correct Value
er = 5;                                                         % Insert Correct Value
Re = 1000;                                                      % Insert Correct Value
fcn = @(x) x+4*log10(er/(3.7*d_i)+1.4125*x/Re);                 % Anonymous Function
x_val = fzero(fcn, 10.8);                                       % Solution

[Brittany Caughron]

The second solution worked perfectly. Thank you so much!

[Star Strider]

As always, my pleasure!