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Finding and Evaluating a Derivative In Exercises \(13-18,\) find \(f^{\prime}(x)\) and \(f^{\prime}(c) .\) $$ \text{Function} \quad \text {Value of} \quad c $$ $$ f(x)=\frac{\sin x}{x} \quad c=\frac{\pi}{6} $$

Short Answer

Expert verified
The derivative of the function \(f(x)=\frac{\sin x}{x}\) is \(f^{\prime}(x)=\frac{x*\cos(x) - \sin(x)}{x^{2}}\). At \(x = \frac{\pi}{6}\), the derivative is \(f^{\prime}(c)=\frac{\frac{\pi}{6}*\cos(\frac{\pi}{6}) - \sin(\frac{\pi}{6})}{(\frac{\pi}{6})^{2}}\).

Step by step solution

01

Apply the Quotient Rule

The Quotient Rule states that the derivative of \(\frac{u}{v}\) is \(\frac{v*u^{\prime} - u*v^{\prime}}{v^{2}}\). Here, \(u = \sin(x)\) and \(v = x\). \nSo, \(u^{\prime} = \cos(x)\) and \(v^{\prime} = 1\). Substituting these into the Quotient rule gives us:\n \(f^{\prime}(x)=\frac{x*\cos(x) - \sin(x)*1}{x^{2}}\)
02

Simplify the Expression

The expression can be simplified to:\n \(f^{\prime}(x)=\frac{x*\cos(x) - \sin(x)}{x^{2}}\)
03

Substitute \(x=c\)

Substitute \(x\) with \(c = \frac{\pi}{6}\) to find the derivative at \(c\):\n \(f^{\prime}(c)=\frac{\frac{\pi}{6}*\cos(\frac{\pi}{6}) - \sin(\frac{\pi}{6})}{(\frac{\pi}{6})^{2}}\)

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Key Concepts

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

Quotient Rule
When it comes to calculus, differentiating complex functions is a fundamental skill, and the Quotient Rule is a powerful tool! It's specifically used when you have a function that is the division of two other functions. Here's how it rolls out: if you have a function in the form \(f(x) = \frac{u}{v}\), then its derivative \(f'(x)\) is given by the formula \[f'(x) = \frac{v\cdot u' - u\cdot v'}{v^2}\].
The key is to first identify your \(u\) and \(v\), which are the top (numerator) and bottom (denominator) parts of your fraction respectively, and then find their derivatives \(u'\) and \(v'\). After that, just plug into the formula, simplify, and voila— you've mastered the Quotient Rule! One pro tip: keep an eye on simplifying expressions; it can turn a cumbersome fraction into something much more manageable.
Derivative of sin(x)/x
The function \(\frac{\sin(x)}{x}\) can seem intimidating, but fear not—it's just a prime candidate for the Quotient Rule. With \(u = \sin(x)\) and \(v = x\), we calculate their derivatives: \(u' = \cos(x)\) (since the derivative of \(\sin\) is \(\cos\)), and \(v' = 1\) (because the derivative of \(x\) with respect to \(x\) is \(1\)). Apply the Quotient Rule to get \(f'(x)\) as shown in the solution. Notice how the challenge here isn't in crunching numbers but in understanding how to apply the rule. Remember, for every function like this, there's a smooth derivative waiting to be found—just follow the Quotient Rule steps closely.
Simplifying Expressions
After getting your derivative using the Quotient Rule, you might end up with a complicated expression. But we can't stop just yet—simplifying the expression is like cleaning up after a great meal; it's necessary and satisfying. Take the derivative \(\frac{x\cdot \cos(x) - \sin(x)}{x^2}\) for instance. Here's an opportunity to look carefully for common factors in the numerator and denominator, and also to reduce fractions to their lowest terms. In other cases, you might want to factor out common variables, or use trigonometric identities to make things neater. Simplifying might not change the derivative value, but it definitely helps to understand and work further with it. Plus, it's always nicer to look at a tidy mathematical expression!

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Most popular questions from this chapter

Graphical Reasoning A line with slope \(m\) passes through the point \((0,4)\) and has the equation \(y=m x+4 .\) (a) Write the distance \(d\) between the line and the point \((3,1)\) as a function of \(m .\) (b) Use a graphing utility to graph the function \(d\) in part (a). (b) Use a graphing utility to graph the function \(d\) in part (a). Based on the graph, is the function differentiable at every value of \(m ?\) If not, where is it not differentiable?

Think About It Describe the relationship between the rate of change of \(y\) and the rate of change of \(x\) in each expression. Assume all variables and derivatives are positive. \(\begin{array}{llll}{\text { (a) } \frac{d y}{d t}=3 \frac{d x}{d t}} & {\text { (b) } \frac{d y}{d t}=x(L-x) \frac{d x}{d t},} & {0 \leq x \leq L}\end{array}\)

Linear and Quadratic Approximations The linear and quadratic approximations of a function \(f\) at \(x=a\) are $$\begin{array}{l}{P_{1}(x)=f^{\prime}(a)(x-a)+f(a) \text { and }} \\\ {P_{2}(x)=\frac{1}{2} f^{\prime \prime}(a)(x-a)^{2}+f^{\prime}(a)(x-a)+f(a)}\end{array}$$ In Exercises 123 and \(124,\) (a) find the specified linear and quadratic approximations of \(f,(b)\) use a graphing utility to graph \(f\) and the approximations, (c) determine whether \(P_{1}\) or \(P_{2}\) is the better approximation, and (d) state how the accuracy changes as you move farther from \(x=a\) . $$ f(x)=\tan x ; \quad a=\frac{\pi}{4} $$

In your own words, state the guidelines for solving related-rate problems.

A ladder 25 feet long is leaning against the wall of a house (see figure). The base of the ladder is pulled away from the wall at a rate of 2 feet per second. (a) How fast is the top of the ladder moving down the wall when its base is 7 feet, 15 feet, and 24 feet from the wall? (b) Consider the triangle formed by the side of the house, the ladder, and the ground. Find the rate at which the area of the triangle is changing when the base of the ladder is 7 feet from the wall. (c) Find the rate at which the angle between the ladder and the wall of the house is changing when the base of the ladder is 7 feet from the wall.

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