State the derivative formulas for \(\sin ^{-1} x, \tan ^{-1} x\), and \(\sec ^{-1} x\).
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Textbook Solutions for Calculus: Early Transcendentals
Question
Towing a boat A boat is towed toward a dock by a cable attached to a winch that stands 10 ft above the water level (see figure). Let \(\theta\) be the angle of elevation of the winch and let \(\ell\) be the length of the cable as the boat is towed toward the dock.
a. Show that the rate of change of \(\theta\) with respect to \(\ell\) is \(\frac{d \theta}{d \ell}=\frac{-10}{\ell \sqrt{\ell^{2}-100}}\).
b. Compute \(\frac{d \theta}{d \ell}\) when \(\ell\) = 50, 20, and 11 ft.
c. Find \(\lim _{\ell \rightarrow 10^{+}} \frac{d \theta}{d \ell}\), and explain what is happening as the last foot of cable is reeled in (note that the boat is at the dock when \(\ell=10\)).
d. It is evident from the figure that \(\theta\) increases as the boat is towed to the dock. Why, then, is \(d \theta / d \ell\) negative?
Solution
The first step in solving 3.9 problem number trying to solve the problem we have to refer to the textbook question: Towing a boat A boat is towed toward a dock by a cable attached to a winch that stands 10 ft above the water level (see figure). Let \(\theta\) be the angle of elevation of the winch and let \(\ell\) be the length of the cable as the boat is towed toward the dock.a. Show that the rate of change of \(\theta\) with respect to \(\ell\) is \(\frac{d \theta}{d \ell}=\frac{-10}{\ell \sqrt{\ell^{2}-100}}\).b. Compute \(\frac{d \theta}{d \ell}\) when \(\ell\) = 50, 20, and 11 ft.c. Find \(\lim _{\ell \rightarrow 10^{+}} \frac{d \theta}{d \ell}\), and explain what is happening as the last foot of cable is reeled in (note that the boat is at the dock when \(\ell=10\)).d. It is evident from the figure that \(\theta\) increases as the boat is towed to the dock. Why, then, is \(d \theta / d \ell\) negative?
From the textbook chapter Derivatives of Inverse Trigonometric Functions you will find a few key concepts needed to solve this.
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