Chapter 7: Problem 75
For the following exercises, write the equation of the tangent line in Cartesian coordinates for the given parameter \(t\). \(x=e^{\sqrt{t}}, \quad y=1-\ln t^{2}, \quad t=1\)
Short Answer
Expert verified
The equation of the tangent line is \( y = -\frac{4}{e}x + 5 \).
Step by step solution
01
Find Derivatives
To find the equation of the tangent line, we first need the derivatives \( \frac{dx}{dt} \) and \( \frac{dy}{dt} \). For \( x = e^{\sqrt{t}} \), use the chain rule to get: \[ \frac{dx}{dt} = \frac{d}{dt}(e^{\sqrt{t}}) = e^{\sqrt{t}} \cdot \frac{1}{2\sqrt{t}} \]For \( y = 1 - \ln(t^2) \), the derivative is: \[ \frac{dy}{dt} = \frac{d}{dt}(1 - \ln(t^2)) = -\frac{2}{t} \].
02
Calculate Slopes
To find the slope of the tangent line, we use the formula:\[ \frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} \]Substitute the derivatives found:\[ \frac{dy}{dx} = \frac{-\frac{2}{t}}{e^{\sqrt{t}} \cdot \frac{1}{2\sqrt{t}}} = \frac{-4\sqrt{t}}{te^{\sqrt{t}}} \].
03
Evaluate Derivatives at \( t = 1 \)
Substitute \( t = 1 \) into the expressions for \( x \), \( y \), and \( \frac{dy}{dx} \):- For \( x \), \( x(1) = e^{\sqrt{1}} = e \).- For \( y \), \( y(1) = 1 - \ln(1^2) = 1 \).- For the slope: \[ \frac{dy}{dx} \bigg|_{t=1} = \frac{-4}{e} \].
04
Tangent Line Equation
With the point \((e, 1)\) and slope \( -\frac{4}{e} \), the tangent line can be written in the point-slope form:\[ y - y_1 = m(x - x_1) \]Substituting the known values gives:\[ y - 1 = -\frac{4}{e}(x - e) \].
05
Simplify the Equation
Rearrange the equation from the point-slope form: \[ y - 1 = -\frac{4}{e}x + 4 \]This simplifies to:\[ y = -\frac{4}{e}x + 5 \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parametric Equations
A parametric equation expresses the coordinates of the points making up a geometric object as functions of a parameter, often denoted as \( t \). This approach allows the representation of curves that might not be possible with a single Cartesian equation.
In this exercise, the parametric equations are given as:
In this exercise, the parametric equations are given as:
- \(x = e^{\sqrt{t}}\)
- \(y = 1 - \ln t^2\)
Derivative Calculation
The derivative represents the rate at which a function is changing and is key in finding tangent lines to curves at specific points. For parametric equations, we need to find the derivatives \( \frac{dx}{dt} \) and \( \frac{dy}{dt} \).
For the problems given:
For the problems given:
- For \( x = e^{\sqrt{t}} \), using derivative properties for exponential functions gives \( \frac{dx}{dt} = e^{\sqrt{t}} \frac{1}{2\sqrt{t}} \).
- For \( y = 1 - \ln(t^2) \), employing the properties of logarithmic derivatives results in \( \frac{dy}{dt} = -\frac{2}{t} \).
Chain Rule
The chain rule is a fundamental concept in calculus used to differentiate composite functions. It states that the derivative of a composite function is the derivative of the outer function evaluated at the inner function times the derivative of the inner function.
Let's take a look at how it's applied here:
Let's take a look at how it's applied here:
- When calculating \( \frac{dx}{dt} \) for \( x = e^{\sqrt{t}} \), the chain rule allows us to find the derivative effortlessly by considering \( \sqrt{t} \) as the inner function, yielding \( e^{\sqrt{t}} \cdot \frac{1}{2\sqrt{t}} \).
Point-Slope Form
The point-slope form is a popular method for writing the equation of a line when you know a point on the line and its slope. It’s structurally expressed as:\[ y - y_1 = m(x - x_1) \]
\[ y - 1 = -\frac{4}{e}(x - e) \]
This specific form simplifies the process of quickly finding the equation of the tangent line, as it seamlessly incorporates both the slope and coordinates of the known point directly.
- \( m \) represents the slope.
- \((x_1, y_1)\) represents the coordinates of the known point.
\[ y - 1 = -\frac{4}{e}(x - e) \]
This specific form simplifies the process of quickly finding the equation of the tangent line, as it seamlessly incorporates both the slope and coordinates of the known point directly.