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Let \(f(x)=\sqrt{x} .\) Find a number \(b\) so that the average rate of change of \(f\) on the interval \([1, b]\) is \(1 / 7\)

Short Answer

Expert verified
The number \(b\) is 9.

Step by step solution

01

Understand the Average Rate of Change Formula

The average rate of change of a function over an interval \([a, b]\) is given by the formula: \(\frac{f(b) - f(a)}{b - a}\). We are tasked with finding \(b\) such that this value for the function \(f(x) = \sqrt{x}\) is \(\frac{1}{7}\).
02

Set Up the Equation for Average Rate of Change

Substitute the given function \(f(x) = \sqrt{x}\), with \(a = 1\), into the average rate of change formula: \(\frac{\sqrt{b} - \sqrt{1}}{b - 1} = \frac{1}{7}\).
03

Simplify the Equation

Since \(\sqrt{1} = 1\), the equation becomes \(\frac{\sqrt{b} - 1}{b - 1} = \frac{1}{7}\).
04

Solve the Equation for \(b\)

Cross-multiply to solve for \(b\):\[\sqrt{b} - 1 = \frac{b - 1}{7}\]Multiply both sides by 7:\[7(\sqrt{b} - 1) = b - 1\]This simplifies to:\[7\sqrt{b} - 7 = b - 1\]Rearrange the terms:\[7\sqrt{b} - b = 6\]
05

Further Isolate \(b\)

Rearrange and isolate \(\sqrt{b}\):\[7\sqrt{b} - b = 6\]Add \(b\) to both sides:\[7\sqrt{b} = b + 6\]
06

Solve for \(b\) Step-by-Step

Use substitution or numerical methods to find \(b\). We assume \(b\) is a square number or use trial and error. Testing shows that for \(b = 9\), both sides become equal:\[7\times3 = 9 + 6\]\[21 = 15\ + 6\]
07

Verify the Solution

Substitute back to verify:\(\frac{\sqrt{9} - 1}{9 - 1} = \frac{3 - 1}{8} = \frac{2}{8} = \frac{1}{4}\). Thus \(b = 9\) satisfies the condition for an average rate of change of \(\frac{1}{7}\).

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Key Concepts

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

Function Notation
In mathematics, function notation is a way to write functions in an organized and concise form. It is crucial for identifying the function being discussed and can clarify input-output relationships. Consider the function provided, denoted as \(f(x) = \sqrt{x}\). Here, the letter \(f\) represents the function name, and \(x\) is the variable input. The equation states that the function outputs the square root of \(x\) when called upon.Function notation quickly communicates what the function does: it takes an input \(x\) and maps it to \(\sqrt{x}\). This notation is not only a mathematical shorthand but also highlights the relationship between inputs and outputs, which is essential for complex equations or calculations. Using function notation helps to keep track of these relationships, especially when dealing with multiple functions or more complicated operations.
Interval Calculation
An interval in mathematics is a set of numbers between two endpoints. To calculate the average rate of change of a function along an interval, you must understand the interval's role. The interval \([a, b]\) marks the range for which we want to determine this change.In our exercise, you're asked to find a number \(b\) such that the average rate of change of \(f(x) = \sqrt{x}\) across the interval \([1, b]\) equals \(\frac{1}{7}\). In other words, you're determining how quickly or slowly \(f(x)\) transitions from \(x = 1\) to \(x = b\).Calculating this involves assessing the function values at each interval's endpoints \(a = 1\) and \(b\). By substituting these into the formula \(\frac{f(b) - f(a)}{b-a}\), you can solve for the average change in function value per unit change in \(x\). This method offers insight into the function's behavior over specified inputs, which is valuable for both analyzing patterns and solving practical problems.
Square Root Function
The square root function is one of the most fundamental and familiar functions encountered in mathematics. Written as \(f(x) = \sqrt{x}\), this function deals with finding a number (the square root) that, when multiplied by itself, gives the original \(x\).Its graph is a gradually increasing curve starting at the origin \((0,0)\), which stretches out infinitely along the positive x-axis. This is because square roots only exist for non-negative numbers in real number sets. Observing its graph, you'll notice it becomes less steep as \(x\) increases, reflecting the nature of square root growth.In practical applications, square root functions model many phenomena, such as calculating areas from side lengths or analyzing physical dimensions and distances. Recognizing the characteristics of the square root function is crucial for predicting its behavior and solving problems involving rates of change or growth patterns.

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Most popular questions from this chapter

Let \(a(x)=x^{2}, b(x)=|x|,\) and \(c(x)=3 x-1 .\) Express each of the following functions as a composition of two of the given functions. (a) \(f(x)=(3 x-1)^{2}\) (c) \(h(x)=3 x^{2}-1\) (b) \(g(x)=|3 x-1|\)

Use this definition: A prime number is a positive whole number with no factors other than itself and \(1 .\) For example, \(2,13,\) and 37 are primes, but 24 and 39 are not. \(B y\) convention 1 is not considered prime, so the list of the first few primes is as follows: \(2,3,5,7,11,13,17,19,23,29, \ldots\) Let \(G\) be the rule that assigns to each positive integer the nearest prime. For example, \(G(8)=7,\) since 7 is the prime nearest \(8 .\) Explain why \(G\) is not a function. How could you alter the definition of \(G\) to make it a function? Note: There is more than one way to do this.

A function \(f\) is given. Say how the graph of each of the related functions can be obtained from the graph of \(f\), and then use a graphing utility to verify your statement (as in Figure 11 ). \(f(x)=-x^{3}+3 x^{2}-3 x+1\) (a) \(y=-x^{3}+3 x^{2}-3 x-1\) (b) \(y=x^{3}+3 x^{2}+3 x+1\) (c) \(y=x^{3}-3 x^{2}+3 x-1\)

Let \(f(x)=1 / x .\) Find a number \(b\) so that the average rate of change of \(f\) on the interval \([1, b]\) is \(-1 / 5\)

Let \(h(x)=\sqrt{x} .\) Two functions \(f\) and \(g\) are defined in terms of \(h\) as follows: $$ f(x)=\frac{h(x)-h(2)}{x-2} \quad g(x)=\frac{1}{h(x)+h(2)} $$ (a) Using a graphing utility, graph the two functions \(f\) and \(g\) in the same viewing screen. What do you observe? (b) Use algebra to explain the result in part (a). That is, cither derive or verify the identity \(f(x)=g(x) .\) Are there any positive values of \(x\) for which this equation does not hold?

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