(a) Here, $a_{1} = 1,\ b_{1} = - \sqrt{3},\ a_{2} = \sqrt{3},\ b_{2} = 1$ Now, $a_{1}a_{2} + b_{1}b_{2} = 1 \bullet \sqrt{3} + \left( - \sqrt{3} \right) \bullet 1 = 0$ $\therefore\$Lines are perpendicular, $ie,\ \theta = 90{^\circ}$
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