Concepts and Vocabulary
True or False \(\dfrac{d}{dx}\cos x= \sin x\)
True or False \(\dfrac{d}{dx}\tan x=\)\(\cot x\)
True or False \(\dfrac{d^{2}}{dx^{2}}\sin x=-\sin x\)
True or False \(\dfrac{d}{dx}\sin \dfrac{\pi }{3}=\cos \dfrac{\pi}{3}\)
Skill Building
In Problems 5–8, find the derivative of f at \(c\).
\(f(x)=x-\sin x\), \(c=\pi\)
\(f(\theta )=2\sin \theta +\cos \theta\), \(c={\dfrac{\pi }{2}}\)
\(f(\theta )={\dfrac{\cos \theta }{1+\sin \theta }}\), \(c=\dfrac{\pi }{3}\)
\(f(x)={\dfrac{\sin x}{1+\cos x}}\), \(c=\dfrac{5\pi }{6}\)
In Problems 9–38, find \(y^\prime\).
\(y=3\sin \theta -2\cos \theta\)
\(y=4\tan \theta +\sin \theta\)
\(y=\sin x\cos x\)
\(y=\cot x\tan x\)
\(y=t\cos t\)
\(y=t^{2}\tan t\)
\(y=e^{x}\tan x\)
\(y=e^{x}\sec x\)
\(y=\pi \sec u\tan u\)
\(y=\pi u\tan u\)
\(y={\dfrac{\cot x}{x}}\)
\(y={\dfrac{\csc x}{x}}\)
\(y=x^{2}\sin x\)
\(y=t^{2}\tan t\)
\(y=t\tan t-\sqrt{3}\sec t\)
\(y=x\sec x+\sqrt{2}\cot x\)
\(y=\dfrac{\sin \theta }{1-\cos \theta}\)
\(y={\dfrac{x}{\cos x}}\)
\(y={\dfrac{\sin t}{1+t}}\)
\(y={\dfrac{\tan u}{1+u}}\)
\(y=\dfrac{\sin x}{e^{x}}\)
\(y=\dfrac{e^{x}}{\cos x}\)
\(y={\dfrac{\sin \theta +\cos \theta }{\sin \theta -\cos \theta }}\)
\(y={\dfrac{\sin \theta -\cos \theta }{\sin \theta +\cos \theta }}\)
\(y={\dfrac{\sec t}{1+t\sin t}}\)
\(y={\dfrac{\csc t}{1+t\cos t}}\)
\(y=\csc \theta\cot \theta\)
\(y=\tan \theta \cos \theta\)
\(y={\dfrac{1+\tan x}{1-\tan x}}\)
\(y={\dfrac{\csc x-\cot x}{\csc x+\cot x}}\)
In Problems 39–50, find \(y''\).
\(y=\sin x\)
\(y=\cos x\)
\(y=\tan \theta\)
\(y=\sec \theta \)
\(y=t\sin t\)
\(y=t\cos t\)
\(y=e^{x}\sin x\)
\(y=e^{x}\cos x\)
\(y=2\sin u-3\cos u\)
\(y=3\sin u+4\cos u\)
\(y=a\sin x+b\cos x\)
\(y=a\sec\theta +b\tan \theta \)
In Problems 51–56:
\(f(x)=\sin x\) at \((0,0)\)
\(f(x)=\cos x\) at \({\left( \dfrac{\pi }{3},\dfrac{1}{2}\right) }\)
\(f(x)=\tan x\) at \((0,0)\)
\(f(x)=\tan x\) at \({\left( \dfrac{\pi }{4},1\right)}\)
\(f(x)=\sin x+\cos x\) at \({\left( \dfrac{\pi }{4},\sqrt{2}\right)}\)
\(f(x)=\sin x-\cos x\) at \({\left( \dfrac{\pi }{4},0\right) }\)
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In Problems 57-60:
\(f(x)=2\sin x+\cos x\)
\(f(x)=\cos x-\sin x\)
\(f(x)=\sec x\)
\(f(x)=\csc x\)
Applications and Extensions
In Problems 61 and 62, find the nth derivative of each function.
\(f(x)=\sin x\)
\(f(\theta )=\cos \theta \)
What is \({\lim\limits_{h\rightarrow 0}\dfrac{\cos \left( { \dfrac{\pi }{2}}+h\right) -\cos {\dfrac{\pi }{2}}}{h}?}\)
What is \(\lim\limits_{h\rightarrow 0}{\dfrac{\sin (\pi +h)-\sin \pi }{h}?}\)
Simple Harmonic Motion The distance \(s\) (in meters) of an object from the origin at time \(t\) (in seconds) is modeled by the function \(s( t) =\dfrac{1}{8}\cos t\).
Simple Harmonic Motion An object attached to a coiled spring is pulled down a distance \(d=\) \(5~{\text{cm}}\) from its equilibrium position and then released as shown in the figure. The motion of the object at time \( t \) seconds is simple harmonic and is modeled by \(d(t) =-5\cos t\). | |
Rate of Change A large, 8-ft high decorative mirror is placed on a wood floor and leaned against a wall. The weight of the mirror and the slickness of the floor cause the mirror to slip.
Rate of Change The sides of an isosceles triangle are sliding outward. See the figure. | |
Sea Waves Waves in deep water tend to have the symmetric form of the function \(f(x)=\sin x\). As they approach shore, however, the sea floor creates drag which changes the shape of the wave. The trough of the wave widens and the height of the wave increases, so the top of the wave is no longer symmetric with the trough. This type of wave can be represented by a function such as \[ w(x)=\dfrac{4}{2+\cos x}. \]
Source: http://www.crd.bc.ca/watersheds/protection/geology-processes/waves.htm
Swinging Pendulum A simple pendulum is a small-sized ball swinging from a light string. As it swings, the supporting string makes an angle \(\theta\) with the vertical. See the figure. At an angle \(\theta\), the tension in the string is \(T=\dfrac{W}{\cos \theta }\), where \(W\) is the weight of the swinging ball. | |
Restaurant Sales A restaurant in Naples, Florida is very busy during the winter months and extremely slow over the summer. But every year the restaurant grows its sales. Suppose over the next two years, the revenue \(R\), in units of $10,000, is projected to follow the model \[ R=R( t) =\sin t+0.3t+1 \qquad 0 ≤ t ≤ 12 \] where \(t=0\) corresponds to November 1, 2014; \(t=1\) corresponds to January 1, 2015; \(t=2\) corresponds to March 1, 2015; and so on.
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Polarizing Sunglasses Polarizing sunglasses are filters that only transmit light for which the electric field oscillations are in a specific direction. Light gets polarized naturally by scattering off the molecules in the atmosphere and by reflecting off of many (but not all) types of surfaces. If light of intensity \(I_{0}\) is already polarized in a certain direction, and the transmission direction of the polarizing filter makes an angle with that direction, then the intensity \(I\) of the light after passing through the filter is given by Malus’s Law, \(I( \theta ) =I_{0}\cos ^{2}\theta \). | |
If \(y=\sin x\) and \(y^{(n)}\) is the \(n\)th derivative of \(y\) with respect to \(x\) find the smallest positive integer \(n\) for which \(y^{(n)}=y\).
Use the identity \(\sin A-\sin B=2\cos \dfrac{A+B}{2}\sin \dfrac{A-B}{2},\) with \(A=x+h\) and \(B=x\), to prove that \[ \dfrac{d}{dx}\sin x= \lim\limits_{h\rightarrow 0}\dfrac{\sin (x+h)-\sin x}{h}=\cos x \]
Use the definition of a derivative to prove \(\dfrac{d }{dx}\cos x=-\sin x\).
Derivative of \({y=\sec x}\) Use a derivative rule to show that \[ \dfrac{d}{dx}\sec x=\sec x\tan x. \]
Derivative of \(y=csc x\) Use a derivative rule to show that \[ \dfrac{d}{dx}\csc x=-\csc x\cot x. \]
Derivative of \({y=\cot x}\) Use a derivative rule to show that \[ \dfrac{d}{dx}\cot x=-\csc ^{2}x. \]
Let \(f(x)=\cos x\). Show that finding \(f^\prime (0)\) is the same as finding \(\lim\limits_{x\rightarrow 0}{\dfrac{\cos x-1}{x}}\).
Let \(f(x)=\sin x\). Show that finding \(f^\prime (0)\) is the same as finding \(\lim\limits_{x\rightarrow 0}{\dfrac{\sin x}{x}}\).
If \(y=A\sin t+B\cos t\), where \(A\) and \(B\) are constants, show that \(y''+y=0\).
Challenge Problem
For a differentiable function \(f\), let \(f^{\ast }\) be the function defined by \[ f^{\ast }(x)=\lim\limits_{h\rightarrow 0}\frac{f(x+h)-f(x-h)}{h} \]