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Ch. 7 - Logarithmic, Exponential Functions, and Hyperbolic Functions
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.3.61a

61–62. Points of intersection and area
a. Sketch the graphs of the functions f and g and find the x-coordinate of the points at which they intersect.


f(x) = sech x, g(x) = tanh x; the region bounded by the graphs of f, g, and the y-axis

Guida verificata passo dopo passo
1
First, recall the definitions of the hyperbolic functions involved: \(f(x) = \operatorname{sech} x = \frac{1}{\cosh x}\) and \(g(x) = \tanh x = \frac{\sinh x}{\cosh x}\). Understanding their shapes will help in sketching the graphs.
Sketch the graph of \(f(x) = \operatorname{sech} x\), which is an even function with a maximum at \(x=0\) where \(f(0) = 1\), and it approaches 0 as \(x \to \pm \infty\). Then sketch \(g(x) = \tanh x\), an odd function that passes through the origin, increasing from \(-1\) to \(1\) as \(x\) goes from \(-\infty\) to \(\infty\).
To find the points of intersection, set \(f(x) = g(x)\), which means solving the equation \(\operatorname{sech} x = \tanh x\). Rewrite this as \(\frac{1}{\cosh x} = \frac{\sinh x}{\cosh x}\), and simplify to find the values of \(x\) where this holds true.
Simplify the equation to \(1 = \sinh x\). Solve for \(x\) by taking the inverse hyperbolic sine: \(x = \sinh^{-1}(1)\). This gives the x-coordinate of the intersection point(s).
To find the area bounded by the graphs of \(f\), \(g\), and the y-axis, identify the interval of integration from \(x=0\) (the y-axis) to the intersection point found. Set up the integral of the difference between the upper and lower functions over this interval: \(\text{Area} = \int_0^{x_{intersection}} (f(x) - g(x)) \, dx\). This integral will give the bounded area.

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Hyperbolic Functions

Hyperbolic functions like sech(x) and tanh(x) are analogs of trigonometric functions but based on hyperbolas. sech(x) = 1/cosh(x) and tanh(x) = sinh(x)/cosh(x). Understanding their shapes and properties is essential for sketching their graphs and analyzing intersections.
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Asymptotes of Hyperbolas

Points of Intersection

Points of intersection occur where two functions have the same value for the same x-coordinate. To find these points, set f(x) equal to g(x) and solve for x. These points define the boundaries of the region enclosed by the graphs.
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Critical Points

Area Between Curves

The area bounded by two curves and the y-axis can be found by integrating the difference of the functions over the interval defined by their intersection points and the y-axis. This involves setting up definite integrals and understanding which function lies above the other.
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Finding Area Between Curves on a Given Interval