9. Which of the following lines is perpendicular to a line whose slope is undefined?

A. [tex]\( y = x \)[/tex]

B. [tex]\( y = 5 \)[/tex]

C. [tex]\( x = -7 \)[/tex]

D. [tex]\( x = 0 \)[/tex]



Answer :

To determine which of the given lines is perpendicular to a line whose slope is undefined, let's first understand the properties of lines with undefined slopes and their perpendicular counterparts.

A line with an undefined slope is a vertical line. Vertical lines have the general equation [tex]\(x = k\)[/tex], where [tex]\(k\)[/tex] is a constant. The slope of such a line is considered undefined because the change in [tex]\(y\)[/tex] happens without any change in [tex]\(x\)[/tex].

A line perpendicular to a vertical line must be a horizontal line. Horizontal lines have the general equation [tex]\(y = c\)[/tex], where [tex]\(c\)[/tex] is a constant. The slope of a horizontal line is 0, which makes it perpendicular to any vertical line.

Now let's examine each option to determine its slope:

A) [tex]\(y = x\)[/tex]
- This line has a slope of 1 (since it can be written in the form [tex]\(y = mx + b\)[/tex] with [tex]\(m = 1\)[/tex]).
- Not horizontal.

B) [tex]\(y = 5\)[/tex]
- This line has a slope of 0 (it is a horizontal line).
- This is a potential candidate.

C) [tex]\(x = -7\)[/tex]
- This line is a vertical line with an undefined slope.
- Not perpendicular to another vertical line.

D) [tex]\(x = 0\)[/tex]
- This line is also a vertical line with an undefined slope.
- Not perpendicular to another vertical line.

From the above analysis, the line that is perpendicular to a line with an undefined slope (a vertical line) is:

B) [tex]\(y = 5\)[/tex]

Thus, the correct answer is:

B) [tex]\(y = 5\)[/tex]