Assertion (A) : Lines given by \( x = py + q, z = ry + s \) and \( x = p'y + q', z = r'y + s' \) are perpendicular to each other when \( pp' + rr' + 1 = 0 \).
Reason (R) : Two lines \( \vec{r} = \vec{a}_1 + \lambda\vec{b}_1 \) and \( \vec{r} = \vec{a}_2 + \mu\vec{b}_2 \) are perpendicular to each other if \( \vec{b}_1 \cdot \vec{b}_2 = 0 \).