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Find the exact location of all the relative and absolute extrema of each function. \( f(t)=\frac{t^{2}+1}{t^{2}-1} ;-2 \leq t \leq 2, t \neq \pm 1\)

Short Answer

Expert verified
There are no relative or absolute extrema for the function \(f(t)=\frac{t^{2}+1}{t^{2}-1}\) in the interval \(-2 \leq t \leq 2\) with the condition that \(t \neq \pm 1\).

Step by step solution

01

Analyzing the function and finding its domain

The given function is \(f(t)=\frac{t^{2}+1}{t^{2}-1}\). Notice that the function is undefined at \(t = \pm 1\), so we need to keep that in mind when solving for extrema. The domain of this function is \(D = (-\infty, -1) \cup (-1, 1) \cup (1, \infty)\). Since we are only considering the interval \(-2 \leq t \leq 2\), we will focus on the subintervals \([-2, -1) \cup (-1, 1) \cup (1, 2]\).
02

Finding critical points of the function

To find critical points, we must take the first derivative of the function and solve for points where the derivative is either equal to zero or undefined. First, we find the derivative of the function: \(f'(t) = \frac{d}{dt}(\frac{t^2+1}{t^2-1}) = \frac{2t(t^2-1) - 2t(t^2+1)}{(t^2-1)^2}\) Next, we look for points where the derivative is zero or undefined: 1. Solving for values of \(t\) where \(f'(t) = 0\) To find out when the derivative is zero, we just need to analyze the numerator of the derivative (as the denominator will not impact the zeros): \(2t(t^2-1) - 2t(t^2+1) = 0\) Solving this equation gives no real solutions within our interval. Therefore, there are no points where the derivative is zero. 2. Solving for values of \(t\) where \(f'(t)\) is undefined We know that the derivative is undefined at \(t = \pm 1\), which are also the points of discontinuity in the function. Thus, we have two critical points, \(t = -1\) and \(t = 1\).
03

Find extrema using the first and second derivative test, including endpoints

To determine whether the critical points correspond to relative extrema, we analyze the behavior of the first derivative around the critical points for changes in sign (which indicate a local maximum or minimum). 1. Interval \((-2, -1)\): The sign of the derivative is positive, indicating an increasing function on this interval. 2. Interval \((-1, 1)\): The derivative is negative, indicating a decreasing function on this interval. 3. Interval \((1, 2)\): The derivative is positive, indicating an increasing function on this interval. We can see that there is a change in the behavior of the function at the critical points: the function starts increasing in the first interval, then decreases in the second interval and finally increases in the third interval. This indicates that there is a relative maximum at \(t = -1\) and a relative minimum at \(t = 1\). However, since these points are not in the domain of the function, they cannot be considered relative extrema. Next, we evaluate the function at the endpoints, -2 and 2, to check for the existence of absolute extrema. \(f(-2) = \frac{(-2)^2+1}{(-2)^2-1} = \frac{5}{3}\) \(f(2) = \frac{(2)^2+1}{(2)^2-1} = \frac{5}{3}\) Since the function has the same value at -2 and 2 and does not attain any extreme points within the domain, there are no relative extrema in the given interval. Therefore, the function does not have any relative or absolute extrema in the given interval \(-2 \leq t \leq 2\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Critical Points
Understanding critical points is pivotal in determining where a function can have potential maxima or minima. A critical point occurs where the first derivative of a function is either zero or undefined. However, it's important to remember not only to consider where this derivative equals zero.

In the context of the exercise, we find the derivative of the function, which is disastrously discontinuous at \(t = \pm 1\). These points are critical since the derivative does not exist there, hinting at potential extremum points. Nonetheless, in our case, they are not included in the function's domain, so they don't lead to an extrema within the specified interval.
First Derivative Test
The first derivative test is a very useful technique to classify critical points as local maxima, minima, or neither. It involves checking the sign of the derivative before and after the critical point to assess if the function's slope changes from positive to negative (indicative of a local maximum) or negative to positive (indicative of a local minimum).

Applying this to our exercise, we evaluate the regions around our critical points. We note that there is a change in sign, which typically suggests a local extremum. However, because these critical points are at discontinuities and not in the interval, they are excluded from being local extrema. This reinforces the importance of considering the domain.
Second Derivative Test
The second derivative test provides another method for identifying whether a critical point is a local maximum or minimum by using the concavity of the curve at that point. If the second derivative at a critical point is positive, the function is concave up, indicating a local minimum. Conversely, if it's negative, the function is concave down, and we have a local maximum. However, when the second derivative is zero, the test is inconclusive.

In our exercise, we do not apply the second derivative test, as the critical points were at discontinuities of the function. Nonetheless, in different circumstances, this test would be the next step after identifying critical points where the first derivative equals zero.
Function Domain
The domain of a function is the complete set of possible input values (x-values) for which the function is defined. It significantly impacts the identification of extrema since the function must exist at these points within the domain to be considered for maximum or minimum values.

For the function in our exercise, the domain excludes the values \(t = \pm 1\) since the function is undefined at those points. We're also limited to the interval \( -2 \leq t \leq 2 \) by the problem's constraints. When looking for extrema, one must heed these domain restrictions, or you might mistakenly include points that are outside the function's allowable inputs, leading to incorrect conclusions.

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Most popular questions from this chapter

Daily oil production by Pemex, Mexico's national oil company, can be approximated by \(q(t)=-0.022 t^{2}+0.2 t+2.9\) million barrels \(\quad(1 \leq t \leq 9)\) where \(t\) is time in years since the start of \(2000 .^{54}\) At the start of 2008 the price of oil was \(\$ 90\) per barrel and increasing at a rate of \(\$ 80\) per year. \(^{55}\) How fast was Pemex's oil (daily) revenue changing at that time?

A company finds that the number of new products it develops per year depends on the size of its annual R\&D budget, \(x\) (in thousands of dollars), according to the formula $$n(x)=-1+8 x+2 x^{2}-0.4 x^{3}$$ a. Find \(n^{\prime \prime}(1)\) and \(n^{\prime \prime}(3)\), and interpret the results. b. Find the size of the budget that gives the largest rate of return as measured in new products per dollar (again, called the point of diminishing returns).

The demand and unit price for your store's checkered T-shirts are changing with time. Show that the percentage rate of change of revenue equals the sum of the percentage rates of change of price and demand. (The percentage rate of change of a quantity \(Q\) is \(\left.Q^{\prime}(t) / Q(t) .\right)\)

The likelihood that a child will attend a live musical performance can be modeled by $$q=0.01\left(0.0006 x^{2}+0.38 x+35\right) . \quad(15 \leq x \leq 100)$$ Here, \(q\) is the fraction of children with annual household income \(x\) who will attend a live musical performance during the year. \({ }^{66}\) Compute the income elasticity of demand at an income level of \(\$ 30,000\) and interpret the result. HINT [See Example 2.]

If you know how fast one quantity is changing and need to compute how fast a second quantity is changing, what kind of information do you need?

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