dx(t)/dt = -x dy(t)/dt = -y x(0)=5, y(0)=-5.
dx(t)/dt = -x dy(t)/dt = -y, x(0)=5, y(0)=-5.
dx(t)/dt = -x, dy(t)/dt = -y x(0)=5, y(0)=-5.
dx(t)/dt = -x, dy(t)/dt = -y, x(0)=5, y(0)=-5.