Question

20 multiple choice 2 points
if line ( ell ) is perpendicular to line ( m ) and the slope of line ( ell ) is undefined, what is the slope of line ( m )?
( \frac{1}{2} )
( -1 )
0
1
21 multiple choice 2 points
which lines appear perpendicular in the figure?
( overleftrightarrow{cr} ) and ( overleftrightarrow{as} )
( overleftrightarrow{rs} ) and ( overleftrightarrow{ab} )
( overleftrightarrow{ab} ) and ( overleftrightarrow{cd} )
( overleftrightarrow{ab} ) and ( overleftrightarrow{xy} )

Explanation:

Step1: Analyze the slope of line \( \ell \)

A line with an undefined slope is a vertical line.

Step2: Determine the slope of a line perpendicular to a vertical line

A line perpendicular to a vertical line is a horizontal line. The slope of a horizontal line is \( 0 \).

for question 21:
Perpendicular lines intersect at a right - angle (\( 90^{\circ} \)). Line \( \overleftrightarrow{AB} \) is horizontal and line \( \overleftrightarrow{XY} \) is vertical. Horizontal and vertical lines are perpendicular.

• \( \overleftrightarrow{CR} \) and \( \overleftrightarrow{AS} \): These lines are not perpendicular as they do not intersect at \( 90^{\circ} \).
• \( \overleftrightarrow{RS} \) and \( \overleftrightarrow{AB} \): These lines are not perpendicular.
• \( \overleftrightarrow{AB} \) and \( \overleftrightarrow{CD} \): These are parallel lines (both horizontal), not perpendicular.

Answer:

\( 0 \) (the third option)