Ch. 5 - Integration

Briggs - Calculus: Early Transcendentals 3rd Edition

Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook

Briggs 3rd Edition

Ch. 5 - Integration

Problem 5.3.4

Chapter 5, Problem 5.3.4

Let ƒ(𝓍) = c, where c is a positive constant. Explain why an area function of ƒ is an increasing function.

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Step 1: Recognize that the function ƒ(𝓍) = c is a constant function, where c is a positive constant. This means that for any value of 𝓍, ƒ(𝓍) always equals c.

Step 2: Recall the concept of an area function. An area function represents the accumulated area under the curve of ƒ(𝓍) from a starting point to a variable endpoint. Mathematically, this is expressed as A(𝓍) = ∫[a,𝓍] ƒ(t) dt, where a is the starting point and t is the variable of integration.

Step 3: Substitute ƒ(t) = c into the integral. The area function becomes A(𝓍) = ∫[a,𝓍] c dt. Since c is constant, it can be factored out of the integral, resulting in A(𝓍) = c ∫[a,𝓍] dt.

Step 4: Evaluate the integral ∫[a,𝓍] dt. The integral of 1 with respect to t is t, so ∫[a,𝓍] dt = [t] evaluated from a to 𝓍, which simplifies to 𝓍 - a. Therefore, A(𝓍) = c(𝓍 - a).

Step 5: Observe that A(𝓍) = c(𝓍 - a) is a linear function of 𝓍 with a positive slope (since c > 0). As 𝓍 increases, A(𝓍) also increases, which confirms that the area function is an increasing function.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Constant Function

A constant function is a function that always returns the same value, regardless of the input. In this case, ƒ(𝓍) = c means that for any value of 𝓍, the output is the constant c. This characteristic implies that the graph of the function is a horizontal line, which is crucial for understanding how the area under the curve behaves.

Area Under the Curve

The area under the curve of a function represents the integral of that function over a specified interval. For a constant function like ƒ(𝓍) = c, the area can be calculated as the product of the constant value and the width of the interval. As the interval increases, the area also increases linearly, which is key to understanding why the area function is increasing.

Increasing Function

An increasing function is one where, as the input value increases, the output value also increases. In the context of the area function derived from a constant function, since the area grows as the interval expands, the area function is classified as increasing. This means that for any two intervals where the second is larger than the first, the area calculated for the second will always be greater.

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