প্রমাণ কর, \text { (i) }(\vec{A} \cdot \vec{B})^{2}+|(\vec{A} \times \vec{B})|^{2}=A^{2} B^{2} \text { (ii) }(\vec{A} \cdot \vec{B})^{2}-|(\vec{A} \times \vec{B})|^{2}=A^{2} B^{2}\left(\cos ^{2} \theta-\sin ^{2} \theta\right)