Help with Periodic functions

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Hello everyone. I have a question with a system of differential equations. I am trying to solve them using Euler's method. The functions are as follows.

dT1 = @(t,T1,T2) (((Ain*Qin)-((k2*(T1-T2+5))*A2)-((k1*(T1-Tout(t)))*A1))/(Cair*rho*V1));
dT2 = @(t,T1,T2) ((((k2*(T1-T2+5))*A2)-((k3*(T2-Tout(t)))*A3))/(Cair*rho*V2));

Where tout is a periodic function as follows.

Tout = @(t) -10*sin((2*pi*t)/(86400));

and the for loop for Euler's method.

  i=1;
    for i = 1:N-1
      t(i+1) = t(i) + h;
      T1(i+1) = T1(i+1)+h*dT1(t(i),T1(i),T2(i));
      T2(i+1) = T2(i+1)+h*dT2(t(i),T1(i),T2(i));
    end 

The issue im running into is with the plot of T1 and T2. The periodic function is working correctly. But since T1 and T2 are defined with a periodic function, they should also be periodic. However, I am getting a completelely linear response. Any ideas?