(a) If $\vec{a}$, $\vec{b}$ and $\vec{c}$ are three vectors such that $| \vec{a} | = 7$, $| \vec{b} | = 24$, $| \vec{c} | = 25$ and $\vec{a} + \vec{b} + \vec{c} = \vec{0}$, then find the value of $\vec{a} \cdot \vec{b} + \vec{b} \cdot \vec{c} + \vec{c} \cdot \vec{a}$. OR (b) If a line makes angles $\alpha$, $\beta$ and $\gamma$ with x-axis, y-axis and z-axis respectively, then prove that $\sin^2 \alpha + \sin^2 \beta + \sin^2 \gamma = 2$.