# Find a variable to make equation = 0

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Plamen Dimitrov on 5 Jul 2021
Edited: Matt J on 5 Jul 2021 Sorry if the question is of the most newbie kind, but my education is not in english so even searching for explanation of the most basic of math problems is really hard.
I'm struggling with this equation: I need to find for which value of w, the answer (wsr) will be 0.
This is the code I've written so far but ofc it doesnt give me the answer I need so any pointers how to fix are very much appreciated!
syms w
ky = 175;
kob = 0.5;
Tob = 40;
wsr = sqrt(ky^2*(1+ky*kob+w^2*Tob^2)^2) + (w*ky^2*kob*Tob)^2 / (1+ky+kob)^2+w^2*Tob^2

Amit Bhowmick on 5 Jul 2021
use fzero or fsolve to find the roots.

Matt J on 5 Jul 2021
For the data that you have shown, there is no solution. Whenever ky^2*kob*Tob is non-zero, then the only possible location where wsr can be zero is at w=0 because otherwise the numerator will be strictly positive.
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Matt J on 5 Jul 2021
There is no solution for A(w)=0. There is a solution for Re{R(jw)}=0, but you can solve that by hand.