# Solving equation with one variable but it is present in the equation twice

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Hiril Patel on 17 Nov 2022
Commented: Torsten on 17 Nov 2022
Hello,
I can solve equation using pen and paper but I have set of data where i have to apply that equation but the probblem is that the unknow vairable in the equation is presnet twice and i dont know how to do it in matlab, here is the equation in picture,
Now Vout is known and it is the set of data which needs to be converted in to resistance, as you can see this is a wheatstone bridge equation. I would like to find x, i can do it manually on paper but don't know how to do it on matlab.
Thank you fo the help in advance

Torsten on 17 Nov 2022
syms x Vout
eqn = Vout == (0.5 - x/(x+1000))*3.3*128;
x = solve(eqn,x)
x =
x = matlabFunction(x)
x = function_handle with value:
@(Vout)-(Vout.*5.0e+3-1.056e+6)./(Vout.*5.0+1.056e+3)
x(100)
ans = 357.3265

David Hill on 17 Nov 2022
It is easy to just solve for x in your equation and have an equation in Vout.
f=@(Vout)(211200-1000*Vout)./(Vout+211.2);
f(100)
ans = 357.3265
Torsten on 17 Nov 2022
You wrote you could solve the equation for x using pencil and paper. Then do it - this is the result you will get:
x = (211200-1000*Vout)./(Vout+211.2)