Assertion (A) : If $|\vec{a} imes \vec{b}|^2 + |\vec{a} \cdot \vec{b}|^2 = 256$ and $|\vec{b}| = 8$, then $|\vec{a}| = 2$. Reason (R) : $\sin^2 heta + \cos^2 heta = 1$ and $|\vec{a} imes \vec{b}| = |\vec{a}| |\vec{b}| \sin heta$ and $\vec{a} \cdot \vec{b} = |\vec{a}| |\vec{b}| \cos heta$.