Solve Non-linear system - System possible but undetermined

Hello,

I have this code to solve:

syms Theta_1 Theta_2 Theta_3

    l1 = 3
    l2 = 2.2
    l3 = 1 
     a = 2
     b = 0.5
     t = 1
while t<70
    phi_1 = (l1*cos(Theta_1)) + (l2*cos(Theta_2)) + (l3*cos(Theta_3)) - a; %Equation 1
    phi_2 = (l1*sin(Theta_1)) + (l2*sin(Theta_2)) + (l3*sin(Theta_3)) - b; %Equation 2
    phi_3 = Theta_3 - sin(0.05*pi*t);                                      %Equation 3

    phi = [phi_1 phi_2 phi_3];
    Theta = [Theta_1 Theta_2 Theta_3];

    [theta_1 theta_2 theta_3]  = solve(phi,Theta); % SOLVING THE EQUATION 

    %Solving
    Num_theta_1 = vpa(theta_1(2)); %positin Bar 1
    Num_theta_2 = vpa(theta_2(2)); %positin Bar 2
    Num_theta_3 = vpa(theta_3(2)); %positin Bar 3

    %Answers
    Answer_Position_Theta_1(t) = Num_theta_1;
    Answer_Position_Theta_2(t) = Num_theta_2;
    Answer_Position_Theta_3(t) = Num_theta_3;
        t = t+1
end
figure(1)
plot(Answer_Position_Theta_3,'-*r')
figure(2)
plot(Answer_Position_Theta_2,'-*r')
figure(3)
plot(Answer_Position_Theta_1,'-*r')

When I run the simulation, I get the following result: 1. Theta_1

1. Theta_2

1. Theta_3

We can see that Theta_3 is correct! The function Sine. But Theta_1 and Theta_2 have some point out of the way. Probably is is because cos(30) = con(-30). I need to define that point following the other points.

Do you know how could I do? What should I change?

Dank! Cheers!