Cosine of an angle

Hello, We know Cosine (x) = Cosine(-x). I have a set of three equations and three unknowns involving finding l2, m2 and d2. I am only able to get the positive angle as the result (1.5708). How do we obtain negative angle i.e (-1.5708) as a result. Thank you

E4 = (Sk(1)+(r)*cos(l2)*sin(m2))== Sk(1)-unit_vi(1)*d2;
E5 = (Sk(2)+(r)*sin(l2)*sin(m2))== Sk(2)-unit_vi(2)*d2;
E6 = ((Sk(3)-L)+(r)*cos(m2))== Sk(3)-L;
result2 = solve(E4,E5,E6); 
disp(double(result2.l2))
disp(double(result2.m2))
disp(double(result2.d2))

Output:

0

1.5708

3

Currently, I am doing - double(result.m2) to substitute in another equation.

Answer 1

[Star Strider]

Experiment with vpasolve, and specifically Specify Ranges of Solutions .

Answer 2

[Matt J]

As far as I can see, only by changing the equations:

E4 = (Sk(1)-(r)*cos(l2)*sin(m2))== Sk(1)-unit_vi(1)*d2;
E5 = (Sk(2)-(r)*sin(l2)*sin(m2))== Sk(2)-unit_vi(2)*d2;
E6 = ((Sk(3)-L)+(r)*cos(m2))== Sk(3)-L;