6) Consider the forced system below:
x1 = sin(xz) cos(x1) + x3 + u
x2 = -xx2 COs(x1)
V(x) = 3(x2 + x2)
Based on the candidate Lyapunov function, get a control law for feedback u(x1, x2) such that the resulting system is stable (x1(t) > 0).
Demonstrate the result by simulation.