Increasing and Decreasing Intervals Practice Problems

Master function behavior with step-by-step practice problems on increasing, decreasing, and constant intervals. Learn to analyze quadratic and linear functions effectively.

📚Master Function Intervals with Interactive Practice
  • Find increasing and decreasing intervals for quadratic functions like f(x) = 5x² - 25
  • Identify vertex coordinates using the formula x = -b/(2a) for parabolas
  • Determine when functions are constant, increasing, or decreasing on given intervals
  • Analyze domain of positivity and negativity from function graphs
  • Apply interval notation to describe function behavior accurately
  • Solve real-world problems involving function monotonicity and optimization

Understanding Constant Function

Complete explanation with examples

We will say that a function is constant when, as the value of the independent variable X X increases, the dependent variable Y Y remains the same.

Let's assume we have two elements X X , which we will call X1 X1 and X2 X2 , where the following is true: X1<X2 X1<X2 , that is, X2 X2 is located to the right of X1 X1 .

  • When X1 X1 is placed in the domain, the value Y1 Y1 is obtained.
  • When X2 X2 is placed in the domain, the value Y2Y2 is obtained.


The function is constant when: X2>X1 X2>X1 and also \(Y2=Y1).

The function can be constant in intervals or throughout its domain.

Constant Function

Constant Function

Detailed explanation

Practice Constant Function

Test your knowledge with 17 quizzes

Determine the domain of the following function:

A function describing the charging of a computer battery during use.

Examples with solutions for Constant Function

Step-by-step solutions included
Exercise #1

Is the function shown in the graph below decreasing?

yx

Step-by-Step Solution

The graph presented is a straight line. To determine whether the function is decreasing, we need to examine the slope of this line.

The line has a negative slope, as it moves downward from left to right. A function is considered decreasing when its slope is negative.

In formal terms, for a linear function expressed as y=mx+c y = mx + c , if the slope m m is negative, the function is decreasing over its entire domain.

From the graph, it's evident that the line has a negative slope, thus indicating that the function is indeed decreasing.

Therefore, the answer to the problem is Yes.

Answer:

Yes

Exercise #2

Is the function in the graph decreasing?

yx

Step-by-Step Solution

To analyze whether the function in the graph is decreasing, we must understand how the function's behavior is defined by its graph:

  • Step 1: Examine the graph. The graph presented is a horizontal line.
  • Step 2: Recognize the properties of a horizontal line. Horizontally aligned lines correspond to constant functions because the y y -value remains the same for all x x -values.
  • Step 3: Define the criteria for a function to be decreasing. A function decreases when, as x x increases, the value of f(x) f(x) decreases.
  • Step 4: Apply this criterion to the horizontal line. Since the y y -value is constant and does not decrease as x x moves rightward, the function is not decreasing.

Therefore, the function represented by the graph is not decreasing.

Answer:

No

Exercise #3

Is the function in the graph below decreasing?

yx

Step-by-Step Solution

To determine if the function is decreasing, we will analyze the graph visually:

The graph shows a line connecting from the bottom-left to the top-right of the graph area, indicating the line has a positive slope. This type of graph indicates the function is increasing, not decreasing.

A decreasing function means its value goes down as x x increases, which is equivalent to having a negative slope.

Since the graph appears with a positive slope, the function is not decreasing.

Thus, the correct choice to the problem, which asks if the function in the graph is decreasing, is No.

Answer:

No

Exercise #4

Does the function in the graph decrease throughout?

YYYXXX

Step-by-Step Solution

To solve this problem, we'll begin by examining the graph of the function provided:

  • Step 1: Observe the graph from left to right along the x-axis.
  • Step 2: Look for any intervals where the function value (y-coordinate) does not decrease as the x-value increases.
  • Step 3: Pay special attention to segments where the graph might look horizontal or rising.

Upon inspecting the graph, we find:

- There are sections where the function's y-values appear to remain constant or potentially rise as the x-values increase. Specifically, even if the function decreases in major portions, any interval where it doesn't means the function cannot be classified as decreasing throughout.

Thus, the function does not strictly decrease on the entire interval shown. Therefore, the solution to the problem is No.

Answer:

No

Exercise #5

Is the function in the graph decreasing? yx

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Verify the graph's overall path direction
  • Step 2: Confirm if the y-values are decreasing as we proceed from the left side of the graph to the right side (increasing x-values).

Now, let's work through each step:

Step 1: By examining the graph, the red line starts at a higher point on the y-axis and moves downward to a lower point as it moves horizontally across the x-axis from left to right.

Step 2: Since for every point, the red line descends as it progresses from the leftmost point to the rightmost, this indicates a consistent decrease in the y-values.

Therefore, the solution to the problem is Yes, the function in the graph is decreasing.

Answer:

Yes

Frequently Asked Questions

How do you find increasing and decreasing intervals of a quadratic function?

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For a quadratic function f(x) = ax² + bx + c, first find the vertex x-coordinate using x = -b/(2a). If a > 0, the function decreases for x < vertex and increases for x > vertex. If a < 0, the pattern reverses.

What makes a function constant on an interval?

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A function is constant when the y-values remain the same as x increases. Mathematically, if x₁ < x₂ but f(x₁) = f(x₂), then the function is constant on that interval.

What is the difference between domain of positivity and increasing intervals?

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Domain of positivity refers to x-values where f(x) > 0 (function is above x-axis). Increasing intervals refer to x-values where the function rises from left to right. These are completely different concepts.

How do you read increasing and decreasing intervals from a graph?

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Look at the function from left to right: (1) Increasing where the graph goes upward, (2) Decreasing where the graph goes downward, (3) Constant where the graph is horizontal. Mark the x-values where direction changes.

Why is finding the vertex important for quadratic function intervals?

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The vertex represents the turning point of a parabola. For upward-opening parabolas (a > 0), it's the minimum point where the function changes from decreasing to increasing. For downward-opening parabolas (a < 0), it's the maximum where function changes from increasing to decreasing.

Can a linear function have both increasing and decreasing intervals?

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No, a non-horizontal linear function is either always increasing (positive slope) or always decreasing (negative slope) across its entire domain. Only horizontal lines (slope = 0) are constant.

What does interval notation look like for function behavior?

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Use parentheses for open intervals: increasing on (0, ∞) means x > 0. Use brackets for closed intervals when endpoints are included. For example, decreasing on (-∞, 0] includes x = 0.

How do you handle piecewise functions when finding intervals?

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Analyze each piece separately within its defined domain, then combine results. Check for continuity at boundary points and note any jumps or breaks that affect the overall interval classification.

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