Chapter 2: Problem 56
Verify the intermediate value theorem (2.26) for \(f\) on the stated interval \([a, b]\) by showing that if \(f(a) \leq w \leq f(b),\) then \(f(c)=w\) for some \(c\) in \([a, b].\) $$ f(x)=-x^{3} $$
Short Answer
Expert verified
Yes, \(f(c) = w\) for \(c = 0\).
Step by step solution
01
Identify the Function and Interval
The function given is \(f(x) = -x^3\). We need to verify the Intermediate Value Theorem (IVT) for this function on the interval \([a,b]\). Here, we are considering the interval \([a, b]\).
02
Evaluate the Function at the Endpoints
Calculate \(f(a)\) and \(f(b)\) and ensure they satisfy \(f(a) \leq w \leq f(b)\), where \(w\) is a value between \(f(a)\) and \(f(b)\).Since no specific \([a, b]\) is given, assume typical values like \([-2, 2]\) for demonstration:- \(f(a) = f(-2) = -(-2)^3 = 8\)- \(f(b) = f(2) = -(2^3) = -8\)Now, choose \(w\) such that \(-8 \leq w \leq 8\). For example, take \(w = 0\).
03
Check Conditions of the Intermediate Value Theorem
The Intermediate Value Theorem states that if \(f\) is continuous on \([a, b]\), and \(f(a) \leq w \leq f(b)\), then there exists \(c \in [a, b]\) such that \(f(c) = w\).Given \(f(x) = -x^3\), which is a polynomial and hence continuous everywhere, the conditions of the IVT are satisfied.
04
Solve for c
Find \(c\) in \([-2, 2]\) such that \(f(c) = 0\).Solve \(-c^3 = 0\), which gives \(c^3 = 0\) or \(c = 0\).Since \(c = 0\) lies within the interval \([-2, 2]\), the condition \(f(c) = 0 = w\) is satisfied.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Continuous Function
A continuous function is a type of function that does not have any sudden jumps, breaks, or holes at any point within its domain. This means you can draw the graph of a continuous function without lifting your pen off the paper. Understanding continuous functions is crucial because many mathematical theorems, like the Intermediate Value Theorem (IVT), depend on this property.
- In mathematics, continuous functions have outputs that change smoothly as the inputs change smoothly.
- When evaluating if a function is continuous, check if it is smooth across its entire interval.
- A function is continuous if it is continuous at every point in the domain.
Polynomial Function
A polynomial function is a type of mathematical expression that includes variables and coefficients, involving only non-negative integer exponents of the variables. These functions are structured in the form \(f(x) = a_nx^n + a_{n-1}x^{n-1} + ... + a_1x + a_0\), where \(a_n\) to \(a_0\) are constants, and \(n\) is a non-negative integer.
- Polynomials are known for their simple and predictable behavior.
- The degree of a polynomial tells us the highest power of the variable present in the polynomial.
- Polynomial functions are smooth and continuous for all real numbers.
Endpoints Evaluation
Endpoints evaluation refers to computing the values of a function at the boundaries of a given interval. This is crucial when applying the Intermediate Value Theorem, as it requires comparing function values at these endpoints to any intermediate value being considered.
- For the interval \([-2, 2]\), calculating \(f(a)\) and \(f(b)\) gives us the values at these endpoints.
- Using the function \(f(x) = -x^3\), we find:
- \(f(-2) = -(-2)^3 = 8\)
- \(f(2) = -(2)^3 = -8\)
- These calculations help identify the range of values \(w\) can take, ensuring that the Intermediate Value Theorem's conditions are satisfied.
Existence of Solutions
The Intermediate Value Theorem provides a guarantee for the existence of solutions within a specific interval. Given that a function is continuous on a closed interval \([a, b]\), and there exists a number \(w\) such that \(f(a) \leq w \leq f(b)\), the theorem asserts that there must be some \(c\) in \([a, b]\) for which \(f(c) = w\).
- If a continuous function transitions from below \(w\) to above \(w\) within an interval, it must cross \(w\) at some point.
- This crossing point is the solution we seek, often interpreted as the root or zero in numerical problems.
- The IVT does not provide the exact location of \(c\), but it ensures one exists.