how to find the two unknowns from the nonlinear equation

clc
clear all
format compact
syms k lambda c T b t0 theta h
lambda=600; b=3;
theta=0;
c=5;
k=250;
h=1.75;
TC=(k/T)+c*lambda+(lambda*(c*theta+h)*(exp(theta*t0)-theta*t0-1))/(T*(theta)^2)+(lambda*b*(T-t0)^2)/(2*T);
dTCdt0=diff(TC,t0);
dTCdT=diff(TC,T);
[T,t0]=solve(dTCdt0,dTCdT)
t0=subs(t0);
digits(3)
t0=vpa(t0)
T=subs(T);
T=vpa(T)
p=theta*t0;
TC=subs(TC);
digits(3)
TC=vpa(TC);
TC=round(TC)
z=sqrt((2*k*(h+c*theta)*b)/(b+h+(c*theta)))*(sqrt(3800)-137.816)

This is my code. I am unable to get the answer for the above. I got the error while I was running the code.

Error using sym/solve (line 266)

Specify the variable to solve for.

Error in

prababaseEOQ (line 13)

[T,t0]=solve(dTCdt0,dTCdT)

[KSSV]

You have defined theta = 0. And this theta comes in the denominator so the expression TC is NaN. You need to think of this first.

format compact 
syms k lambda c T b t0 theta h



TC=(k/T)+c*lambda+(lambda*(c*theta+h)*(exp(theta*t0)-theta*t0-1))/(T*(theta)^2)+(lambda*b*(T-t0)^2)/(2*T);

dTCdt0=diff(TC,t0);
dTCdT=diff(TC,T);

[Dyuman Joshi]

You did not specify which variables are the unknowns.

What are the equations you are attempting to solve?

Why define variables as symbolic, just to overwrite them with numerical values?

[M.Rameswari Sudha]

I changed the theta value 0 to 0.02. I got the answer. Thank you KSSV.