Chapter 15: Problem 31
Exer. 29-32: Find the points on the graph of the equation at which the curvature is \(0 .\) $$ y=\sinh x $$
Short Answer
Expert verified
The point of zero curvature is (0, 0).
Step by step solution
01
Find the First Derivative
The given function is \( y = \sinh x \). The first derivative of \( y \) with respect to \( x \) is found using the derivative of hyperbolic sine function. We have: \( \frac{dy}{dx} = \cosh x \).
02
Find the Second Derivative
Next, we compute the second derivative which is the derivative of \( \frac{dy}{dx} = \cosh x \). So, \( \frac{d^2y}{dx^2} = \sinh x \).
03
Calculate the Curvature
Curvature \( \kappa \) for a function \( y = f(x) \) is given by the formula: \[ \kappa = \frac{|f''(x)|}{(1 + (f'(x))^2)^{3/2}} \] Substituting \( f'(x) = \cosh x \) and \( f''(x) = \sinh x \), the curvature is \( \kappa = \frac{|\sinh x|}{(1 + (\cosh x)^2)^{3/2}} \).
04
Set Curvature to Zero
For the curvature to be zero, the numerator of the curvature formula must be zero. Therefore, \( |\sinh x| = 0 \). Since \( \sinh x = 0 \) when \( x = 0 \), the point on the graph where the curvature is zero is when \( x = 0 \).
05
Find the Corresponding y-coordinate
When \( x = 0 \), substitute back into the original function to find \( y \): \( y = \sinh(0) = 0 \). Thus, the point of zero curvature on the graph is \( (0, 0) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hyperbolic Functions
Hyperbolic functions may seem a bit unfamiliar at first, but they are quite analogous to trigonometric functions. The hyperbolic sine function, denoted as \( \sinh x \), is one such function and can be described as:
- Related to the exponential function: \( \sinh x = \frac{e^x - e^{-x}}{2} \).
- Unlike trigonometric functions, hyperbolic functions are defined for all real numbers.
- The graph of \( \sinh x \) wiggles around the x-axis but doesn't oscillate between fixed values like sine does.
Derivative
The derivative is a fundamental tool in calculus. It provides us with the rate at which a function is changing at any point. For hyperbolic functions, such as \( y = \sinh x \), knowing how to find the derivative is crucial. Here’s the key takeaway:
- The derivative of \( \sinh x \) is \( \cosh x \).
- This results from the definition of hyperbolic functions, where \( \cosh x = \frac{e^x + e^{-x}}{2} \).
Second Derivative
If the first derivative tells you the slope, the second derivative gives information about how that slope itself is changing. This is particularly important in understanding curvature.
- For \( y = \sinh x \), the second derivative is the derivative of \( \cosh x \).
- Deriving \( \cosh x \) gives us \( \sinh x \) again, coming full circle.
Graph Analysis
Graph analysis is not only about sketching a function but understanding its properties such as curvature. For the function \( y = \sinh x \), here's how we use derivatives:
- Curvature \( \kappa \) is calculated using both the first and the second derivatives.
- For \( y = \sinh x \), \( \kappa \) becomes zero when \( \sinh x = 0 \), specifically at \( x = 0 \).
- At this point, the graph has no bending, lying flat against the tangent.