Question

What is the slope of any line parallel to the y-axis in the

(x, y) coordinate plane?
F. -1
G. O
H. 1
J. Undefined
K. Cannot be determined from the given information

Answer 1

A line parallel to the y-axis in the (x, y) coordinate plane is undefined.

• Hence, option J is correct.

Explanation:

We know that the slope of a vertical line on a coordinate plane is undefined.

We also know that a line parallel to the y-axis is basically a vertical line.

Therefore, a line parallel to the y-axis in the (x, y) coordinate plane is undefined.

• Hence, option J is correct.

EXAMPLE

For example, considering the two points of a line

(x₁, y₁) = (1, 3)

(x₂, y₂) = (1, 5)

Determining the slope between (1, 3) and (1, 5)

Using the formula

Slope = m = [y₂ - y₁] / [x₂ - x₁]

= [5 - 3] / [1 - 1]

= 2/0

= ∞ or undefined

Thus, the slope of the line = m = undefined

Thus, the equation of a line parallel to y-axis passing through the points (1, 3) and (1, 5) will be:

• x = 1

Please also check the attached graph.