Chapter 4: Problem 18
Find all values of c that satisfy the Mean Value Theorem for Integrals on the given interval. $$ f(x)=x(1-x) ; \quad[0,1] $$
Short Answer
Expert verified
Values of c: \(c = \frac{3 + \sqrt{3}}{6}\), \(c = \frac{3 - \sqrt{3}}{6}\).
Step by step solution
01
Determine the Integral of the Function
The Mean Value Theorem for integrals states that if a function is continuous on a closed interval \([a, b]\), there exists at least one number \(c\) in \([a, b]\) such that \(f(c) = \frac{1}{b-a} \int_{a}^{b} f(x) \, dx\). First, we need to calculate the integral of \(f(x) = x(1-x)\) over the interval \([0,1]\). Compute the integral: \[\int_{0}^{1} x(1-x) \, dx\]
02
Calculate the Indefinite Integral
Find the indefinite integral of \(f(x) = x(1-x)\). Expand the expression: \[x(1-x) = x - x^2\]Now integrate term by term: \[\int x - x^2 \, dx = \frac{x^2}{2} - \frac{x^3}{3} + C\]
03
Evaluate the Definite Integral
Evaluate the definite integral of the function over \([0, 1]\):\[\int_{0}^{1} \left( x - x^2 \right) \, dx = \left[ \frac{x^2}{2} - \frac{x^3}{3} \right]_{0}^{1}\]Computing this gives:\[\left( \frac{1^2}{2} - \frac{1^3}{3} \right) - \left( \frac{0^2}{2} - \frac{0^3}{3} \right) = \frac{1}{2} - \frac{1}{3} = \frac{1}{6}\]
04
Calculate the Value of the Average Height of the Function
According to the Mean Value Theorem for Integrals, find \( f(c) \) such that:\[f(c) = \frac{1}{b-a} \cdot \int_{0}^{1} f(x) \, dx = 1 \cdot \frac{1}{6} = \frac{1}{6}\]The value of \( f(c) \) is \(\frac{1}{6}\).
05
Solve for c in f(c) = 1/6
The function \(f(c)\) is given as \(f(x) = x - x^2\). Set \(f(c) = \frac{1}{6}\):\[c - c^2 = \frac{1}{6}\]Re-arrange this to:\[c^2 - c + \frac{1}{6} = 0\]This is a quadratic equation in standard form.
06
Use the Quadratic Formula
Use the quadratic formula \(c = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\) to solve for \(c\):- For \(a = 1\), \(b = -1\), \(c = \frac{1}{6}\), substitute into the formula:\[c = \frac{-(-1) \pm \sqrt{(-1)^2 - 4 \cdot 1 \cdot \frac{1}{6}}}{2 \cdot 1} \]Simplify the expression:\[c = \frac{1 \pm \sqrt{1 - \frac{2}{3}}}{2} = \frac{1 \pm \sqrt{\frac{1}{3}}}{2}\]
07
Simplify the Solution
Further simplify to find \(c\):\[c = \frac{1 \pm \frac{1}{\sqrt{3}}}{2}\]Rationalize the denominator of the term involving square root:\[c = \frac{1 \pm \frac{\sqrt{3}}{3}}{2} = \frac{3 \pm \sqrt{3}}{6}\]Thus, the critical values of \(c\) are \(c = \frac{3 + \sqrt{3}}{6}\) and \(c = \frac{3 - \sqrt{3}}{6}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Continuous Function
In calculus, a continuous function is pivotal for understanding derivatives, integrals, and many theorems like the Mean Value Theorem (MVT) for Integrals. A function is continuous over an interval \( [a, b] \) if, intuitively, its graph can be drawn without lifting a pencil from the paper. There are no breaks, jumps, or holes.
For the Mean Value Theorem for Integrals to apply, the function must be continuous on the closed interval \( [a, b] \). This ensures that there will exist at least one value \( c \) in the interval where the function's average value equals the function value. In the given problem, \( f(x) = x(1-x) \), this quadratic function is continuous over the interval \( [0, 1] \), fulfilling the criteria for applying the theorem.
For the Mean Value Theorem for Integrals to apply, the function must be continuous on the closed interval \( [a, b] \). This ensures that there will exist at least one value \( c \) in the interval where the function's average value equals the function value. In the given problem, \( f(x) = x(1-x) \), this quadratic function is continuous over the interval \( [0, 1] \), fulfilling the criteria for applying the theorem.
Definite Integral
The definite integral is a fundamental concept in calculus that accumulates the values of a function over a specified interval. It represents the area under the curve of the function from one point to another. For a function \( f(x) \) with respect to \( x \), the definite integral over the interval \( [a, b] \) is denoted by \[ \int_{a}^{b} f(x) \, dx \].
To calculate a definite integral like \( \int_{0}^{1} x(1-x) \, dx \), you first find the antiderivative or indefinite integral. Then, you evaluate this antiderivative at the boundaries of the interval and find the difference.
To calculate a definite integral like \( \int_{0}^{1} x(1-x) \, dx \), you first find the antiderivative or indefinite integral. Then, you evaluate this antiderivative at the boundaries of the interval and find the difference.
- The process of calculating definite integrals often involves fundamental techniques of integration like substitution or integration by parts, but in this problem, direct polynomial integration suffices.
- In practice, definite integrals allow us to calculate physical properties like areas under curves, volumes, and other aggregated measures.
Quadratic Formula
The quadratic formula is a powerful tool for finding solutions to quadratic equations, which are equations of the form \[ ax^2 + bx + c = 0 \]. These equations often arise in problems across various fields, including physics, engineering, and economics. The quadratic formula is expressed as:
\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]- The term \( b^2 - 4ac \) is called the discriminant.- It determines the nature of the roots: * If positive, there are two distinct real solutions. * If zero, one real solution exists. * If negative, the roots are complex or imaginary.In the context of the original problem, finding \( c \) required solving a quadratic equation derived from equating the function value \( f(c) \) to the average value over the interval. The solutions provide the specific \( c \) values satisfying the Mean Value Theorem.
\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]- The term \( b^2 - 4ac \) is called the discriminant.- It determines the nature of the roots: * If positive, there are two distinct real solutions. * If zero, one real solution exists. * If negative, the roots are complex or imaginary.In the context of the original problem, finding \( c \) required solving a quadratic equation derived from equating the function value \( f(c) \) to the average value over the interval. The solutions provide the specific \( c \) values satisfying the Mean Value Theorem.
Indefinite Integral
The indefinite integral, also known as an antiderivative, represents a family of functions whose derivative gives the original function. In symbol form, the indefinite integral of \( f(x) \) with respect to \( x \) is written as \[ \int f(x) \, dx \. \] An arbitrary constant \( C \) is always added to denote the constant of integration since differentiation of any constant is zero.- Finding the indefinite integral is akin to reversing the process of differentiation.- It provides the general form from which we can derive specific solutions by applying initial conditions or boundaries.- For example, the indefinite integral of \( x - x^2 \) would be \[ \frac{x^2}{2} - \frac{x^3}{3} + C \. \]In the given problem, calculating the indefinite integral is a step in determining the definite integral, which plays a critical role in solving the Mean Value Theorem for Integrals. The indefinite integral is evaluated over specific limits to find the definite integral.