Consider two solutions x(t) = x₁(t) and x(t) = x₂ (t) of the differential equation ^{$\frac{d^2x(t)}{dt^2}$} + x (t) = 0, t > 0, such that x₁ (0) = 1,^{$\frac{dx_1(t)}{dt} \Big|{t -0} = 0, x_2(0) = 0, \frac{dx_2(t)}{dt}\Big|{t-0}$} = 1

The Wronskian W (t) = ^{$\begin{bmatrix} \ x_1(t) & x_2(t) \ \ \frac{dx_1(t)}{dt} & \frac{dx_2(t)}{dt} \ \end{bmatrix}$} at t = ^{$\frac{\pi}{2}$} is