The direction ratios of a line are determined by:

a) Ratios of its equation coefficients

b) Components of its direction vector

c) Ratios of its coordinates

d) Components of its equation

If two lines are perpendicular, what can be said about their direction ratios?

a) Their dot product is zero.

b) Their cross product is zero.

c) The sum of their direction ratios is zero.

d) The difference of their direction ratios is zero.

What is the formula for finding the angle between two lines with direction cosines \( l_1, m_1, n_1 \) and \( l_2, m_2, n_2 \)?

a) \( \cos^{-1}(l_1 l_2 + m_1 m_2 + n_1 n_2) \)

b) \( \cos^{-1}(l_1 + m_1 + n_1 + l_2 + m_2 + n_2) \)

c) \( \cos^{-1}\left(\frac{l_1 l_2 + m_1 m_2 + n_1 n_2}{\sqrt{l_1^2 + m_1^2 + n_1^2} \sqrt{l_2^2 + m_2^2 + n_2^2}}\right) \)

d) \( \cos^{-1}\left(\frac{l_1 + m_1 + n_1}{l_2 + m_2 + n_2}\right) \)

Which equation represents the vector equation of a line parallel to the vector \( \langle 1, -2, 3 \rangle \) passing through the point \( (4,5,6) \)?

a) \( r = \langle 4,5,6 \rangle + \lambda \langle 1,-2,3 \rangle \)

b) \( r = \langle 4,5,6 \rangle + \lambda \langle -1,2,-3 \rangle \)

c) \( r = \langle 1,-2,3 \rangle + \lambda \langle 4,5,6 \rangle \)

d) \( r = \langle 4,5,6 \rangle + \lambda \langle 3,2,-1 \rangle \)

Skew lines are lines that:

a) Are parallel but do not intersect.

b) Lie in the same plane but do not intersect.

c) Are not coplanar and do not intersect.

d) Intersect at a right angle.

Skew lines are:

a) Parallel lines

b) Coplanar lines

c) Intersecting lines

d) Non-intersecting and non-parallel lines

Which equation represents the Cartesian equation of a line passing through points \( P(1,2,3) \) and \( Q(4,5,6) \)?

a) \( \frac{x-1}{3} = \frac{y-2}{3} = \frac{z-3}{3} \)

b) \( \frac{x-1}{4} = \frac{y-2}{5} = \frac{z-3}{6} \)

c) \( \frac{x-1}{3} = \frac{y-2}{3} = \frac{z-3}{4} \)

d) \( \frac{x-1}{4} = \frac{y-2}{5} = \frac{z-3}{6} \)

What do the direction cosines of a line indicate?

a) The angles between the line and the coordinate axes.

b) The ratios of the direction components of the line.

c) The perpendicular distances from the line to the coordinate axes.

d) The inclinations of the line with the coordinate axes.