# Undefined Slope

## Understanding Undefined Slope

The slope of a line helps us understand the steepness of a line. An undefined slope hints at a situation where we can not express the slope of a line as a finite number value. The slope of a line is typically calculated as the ratio of the change in vertical direction (also called “rise”)  to the change in horizontal direction (also called “run”). Undefined slope happens when there is no change in horizontal direction across any points on a line. If the run is zero, we cannot calculate the ratio of rise to run because division by zero is undefined in mathematics. More precisely, we can say that all vertical lines have undefined slope.
Imagine a line or curve that goes up or down so much that it almost looks like a wall. That's what we mean by undefined slope. In this article, we'll dive into what an undefined slope means in more detail, including how to spot it on graphs. We'll also work through some examples together to help you understand it better.

## Defining Undefined Slope

The undefined slope of a line happens when its steepness can't be figured out or expressed as a regular number. For example, imagine a line that goes straight up or down on a graph—it's so steep that we can't measure it as we do with other lines.

One way to calculate slope is by looking at the angle the line makes with the x-axis. But for a vertical line, like one that runs straight up and down, that angle is 90 degrees, and the tangent of 90 degrees is undefined.

Another way to find slope is by comparing how much the line goes up or down (the "rise") to how much it goes sideways (the "run"). But for a vertical line, there's no sideways movement across two points at all, so the "run" is zero. When we try to divide by zero, we end up with an undefined slope.

## Explaining Slope Calculation

To find the slope of a line, we compare how much it goes up or down (the vertical change) to how much it goes left or right (the horizontal change). This is done by taking the difference in the vertical or y values (Δy) and dividing it by the difference in the horizontal or x values (Δx).
The slope of a line = \frac{Δy}{Δx}

However, when the line doesn't move left or right at all, meaning there's no change in the horizontal values (x), the slope becomes undefined. In simpler terms, if the line is perfectly vertical, its slope can't be determined using this method.

Let's consider an example to understand the undefined slope better:

Example : Fine the slope of the line passing through (2, 3) and (2, 5).

Solution:

The slope of a line   = \frac{Δy}{Δx}

Here

$$Δy = 5 - 3 = 2$$
$$Δx = 2 - 2 = 0$$

If we try to calculate the slope using these values we get  \frac{2}{0} .

We end up with an undefined result because the denominator (the difference in horizontal values) is zero.

## Explaining the Equation for Undefined Slope

When a line has an undefined slope, it means it's going straight up and down, parallel to the y-axis. This creates a 90-degree angle with the x-axis, where the tangent is undefined.

The equation for such a line is x = a, where a represents the x-coordinate of the point where the line crosses the x-axis. In simpler terms, this equation tells us that no matter where we look along the line, the x-coordinate remains the same. So, if you're dealing with a line that shoots straight up or down, you'll likely encounter the undefined slope equation x = a.

## Understanding the Graph of Undefined Slope

When we talk about the undefined slope graph, we're referring to lines that go straight up and down, parallel to the y-axis. These lines don't intersect the y-axis, so we can't find any y-intercept for them. Because of this, we can't express these lines using the intercept form.

Graphically, an undefined slope is represented by perfectly vertical lines on a graph. For undefined slope example, if we look at lines like x = -4, x = 2 and x = 8, they all show undefined slopes because they shoot straight up or down without any tilt to the left or right.

## Explaining How to Identify Undefined Slope

Finding the undefined slope doesn't involve any calculations because it's already inherent in the equation of the line. Here are the steps to find the undefined slope:

1. Look for any equation in the form x = a, where a is a constant.

2. Recognize that such an equation represents a vertical line with an undefined slope.

3. Understand that when the slope is undefined, it indicates that the line is vertical and runs parallel to the y-axis.

4. Visualize the undefined slope as a line perpendicular to the x-axis, forming a 90-degree angle.

5. Remember that the defining feature of an undefined slope is that its steepness cannot be expressed by a single numerical value.

## Contrasting Zero Slope and Undefined Slope

It is important to understand that while vertical lines have undefined slope, horizontal lines lines have zero slope. This is because for a horizontal line, the change in x values is zero. This makes the run zero, making the ratio of rise over run equal to 0. Therefore, slope of any horizontal line is 0.

## Solved Examples

Example 1: Identify the slope of the line represented by the equation  x = -2 .

Solution:

The equation  x = -2  represents a vertical line where the value of  x  remains constant regardless of the value of  y . Therefore, this line has an undefined slope.

Example 2: Find the slope of the line passing through the points  (2, -5)  and  (2, 3) .

Solution:

Given the points  (2, -5)  and  (2, 3) , the change in  x  is  2 - 2 = 0 , and the change in  y  is  3 - (-5) = 8 . Therefore, the slope  m  is calculated as:

m = \frac{\Delta y}{\Delta x} = \frac{8}{0}

As the denominator is zero, the slope is undefined.

Example 3: Draw the graph for the line  x = 4   and find its slope.

Solution:

Since the equation  x = 4  represents a vertical line, the slope of the line is undefined.

Example 4: Find the slope of the graph given below.

Solution:

The slope of the graph is undefined.

Example 5: Determine whether the line represented by the equation is a zero slope or an undefined slope.

 y = 3

Solution:

The equation  y = 3  represents a horizontal line where the value of  y  remains constant regardless of the value of  x . Therefore, this line has a zero slope.

## Practice Problems

Q1. True or False: A vertical line has a slope of zero.

1. True
2. False

Q2. Which of the following equations represents a vertical line?

1.  y = 3x + 2
2.  x = 5
3.  y = 2

Q3. Which of the following is the equation of a vertical line passing through (5,-6)?

1.  y = -2x + 5
2.  y = 7
3.   x = 5

Q4. Identify the slope of the line  x = 34 .

1. 0
2. Undefined
3. (3)/(4)
4. (4)/(3)

Q5. Which of the following equations represents a line parallel to the y-axis?

1.  y = -5x + 3
2.  x = 4
3.  y = 2x + 7

Q1. What is an undefined slope?

Answer: An undefined slope refers to the slope of a vertical line. It occurs when the change in the vertical direction becomes infinitely large compared to the horizontal direction. In mathematical terms, the slope is undefined when the denominator of the slope formula is zero, which happens for vertical lines.

Q2. How do you find the slope of a line?

Answer: The slope of a line is typically calculated as the ratio of the change in the vertical direction (the "rise") to the change in the horizontal direction (the "run") between two points on the line. This is represented by the formula:
slope = \frac{\Delta y}{\Delta x} .

Q3. What is a zero slope?

Answer: A zero slope refers to the slope of a horizontal line. It occurs when there is no change in the vertical direction (the "rise") between any two points on the line. In mathematical terms, the slope is zero when the numerator of the slope formula is zero.

Q4. How do you draw an undefined slope graph?

Answer: To graph a line with an undefined slope, such as a vertical line, you plot points that have the same x-coordinate and then connect them with a straight line. This line will be vertical and parallel to the y-axis.

Q5. Can a line have both zero and undefined slopes?

Answer: No, a line cannot have both zero and undefined slopes simultaneously. A line with a zero slope is horizontal, while a line with an undefined slope is vertical. These are two distinct cases, and a line can only have one type of slope at a time.