Chapter 17: Problem 15
Draw a sketch of the graph of the given vector equation and find a cartesian equation of the graph. $$ \mathbf{R}(t)=3 \cosh t \mathbf{i}+5 \sinh t \mathbf{j} $$
Short Answer
Expert verified
The Cartesian equation is \[ \frac{x^2}{9} - \frac{y^2}{25} = 1. \ The graph is a hyperbola.
Step by step solution
01
- Understand the vector equation
The given vector equation is \[ \mathbf{R}(t)=3 \cosh t \mathbf{i}+5 \sinh t \mathbf{j} \. \] Here, \[ \cosh t \] and \[ \sinh t \] represent hyperbolic cosine and hyperbolic sine functions, respectively. These functions describe the x and y components of the vector as functions of the parameter t.
02
- Express the components separately
Write the components of the vector equation separately: \[ x = 3 \cosh t \] and \[ y = 5 \sinh t. \]
03
- Use hyperbolic function identities
Recall the identity for hyperbolic functions: \[ \cosh^2 t - \sinh^2 t = 1. \]
04
- Substitute hyperbolic functions' expressions
Express \[ \cosh t \] and \[ \sinh t \] in terms of x and y: \[ \cosh t = \frac{x}{3} \] and \[ \sinh t = \frac{y}{5}. \]
05
- Form the Cartesian equation
Substitute \[ \cosh t = \frac{x}{3} \] and \[ \sinh t = \frac{y}{5} \] into the hyperbolic identity: \[ \left( \frac{x}{3} \right)^2 - \left( \frac{y}{5} \right)^2 = 1. \]
06
- Simplify the Cartesian equation
Simplify the equation: \[ \frac{x^2}{9} - \frac{y^2}{25} = 1. \] This is the Cartesian equation of the given vector equation.
07
- Sketch the graph
The Cartesian equation \[ \frac{x^2}{9} - \frac{y^2}{25} = 1 \] represents a hyperbola. Sketch the graph by identifying the vertices and asymptotes of the hyperbola.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hyperbolic Functions
Hyperbolic functions are analogs of trigonometric functions but for a hyperbola rather than a circle. They are essential in various areas of calculus and complex analysis. The two primary hyperbolic functions are hyperbolic cosine, \(\textrm{cosh}(t)\), and hyperbolic sine, \(\textrm{sinh}(t)\).
Hyperbolic cosine and sine are defined as follows:
These functions have several useful identities, one of which is:
\[ \textrm{cosh}^2(t) - \textrm{sinh}^2(t) = 1. \]
This identity is crucial for converting vector equations with hyperbolic functions into Cartesian equations.
Hyperbolic cosine and sine are defined as follows:
- \(\textrm{cosh}(t) = \frac{e^t + e^{-t}}{2}\)
- \(\textrm{sinh}(t) = \frac{e^t - e^{-t}}{2}\)
These functions have several useful identities, one of which is:
\[ \textrm{cosh}^2(t) - \textrm{sinh}^2(t) = 1. \]
This identity is crucial for converting vector equations with hyperbolic functions into Cartesian equations.
Cartesian Equation
A Cartesian equation is a way to describe curves using only the Cartesian coordinates \(x\text{ and }y\). It eliminates any parameter, like \(t\), by expressing the relationship between \(x\text{ and }y\) directly.
In the context of the given vector equation:
\[ \textbf{R}(t) = 3 \textrm{cosh}(t) \textbf{i} + 5 \textrm{sinh}(t) \textbf{j}, \]
the components can be isolated as:
Using the hyperbolic identity \( \textrm{cosh}^2(t) - \textrm{sinh}^2(t) = 1 \), we can express this as:
\[ \frac{x^2}{9} - \frac{y^2}{25} = 1. \]
This is a Cartesian equation that represents a hyperbola.
In the context of the given vector equation:
\[ \textbf{R}(t) = 3 \textrm{cosh}(t) \textbf{i} + 5 \textrm{sinh}(t) \textbf{j}, \]
the components can be isolated as:
- \( x = 3 \textrm{cosh}(t) \)
- \( y = 5 \textrm{sinh}(t) \)
Using the hyperbolic identity \( \textrm{cosh}^2(t) - \textrm{sinh}^2(t) = 1 \), we can express this as:
\[ \frac{x^2}{9} - \frac{y^2}{25} = 1. \]
This is a Cartesian equation that represents a hyperbola.
Hyperbola Graphing
Graphing a hyperbola requires understanding its standard Cartesian form. For the hyperbola given by the equation \[ \frac{x^2}{9} - \frac{y^2}{25} = 1, \] the key elements to identify are its vertices and asymptotes.
In this equation:
To sketch the hyperbola, first plot the vertices at \( (\text{±}3 \text{,0}) \), draw the asymptote lines through the origin with slopes \( \text{±} \frac{5}{3} \), and then sketch the branches of the hyperbola opening along these asymptotes. The hyperbola will extend infinitely along these branches while getting increasingly closer to the asymptotes.
In this equation:
- \textbf{Vertices}: The vertices are located at \( ( \text{±}\frac{A} \text{,0} ) \), where \( A \) is the square root of the denominator under the \(x^2\) term, in this case, \( A = 3 \). So, the vertices are at \( (\text{±}3 \text{,0}) \).
- \textbf{Asymptotes}: The asymptotes are the lines along which the hyperbola approaches infinity. For hyperbolas of this form, the asymptotes are given by:
\[ y = \text{±} \frac{B}{A} x, \]
where \( B \) is the square root of the denominator under the \(y^2\) term, here \( B = 5 \). Thus, the asymptotes are \( y = \text{±} \frac{5}{3} x. \)
To sketch the hyperbola, first plot the vertices at \( (\text{±}3 \text{,0}) \), draw the asymptote lines through the origin with slopes \( \text{±} \frac{5}{3} \), and then sketch the branches of the hyperbola opening along these asymptotes. The hyperbola will extend infinitely along these branches while getting increasingly closer to the asymptotes.