Vector Algebra

Let \(\mathbf{a}, \mathbf{b}\) and \(\mathbf{c}\) be three-unit vectors and \(\mathbf{a} \cdot \mathbf{b}=\mathbf{a} \cdot \mathbf{c}=0\). If the angle between \(\mathbf{b}\) and \(\mathbf{c}\) is \(\frac{\pi}{3}\). Then \([\mathbf{a b c}]^2\) is equal to