Chapter 3: Problem 38
a. Find an equation of the tangent line at \(x=a\) b. Use a graphing utility to graph the curve and the tangent line on the same set of axes. \(y=\frac{e^{x}}{4}-x ; a=0\)
Short Answer
Expert verified
Answer: The equation of the tangent line at \(x=0\) is \(y=\frac{1}{4}-\frac{3}{4}x\).
Step by step solution
01
Find the derivative of \(y(x)\)
First, we find the derivative of the given function \(y(x)=\frac{e^x}{4}-x\) with respect to \(x\). Use the properties of derivatives:
\(y'(x) = \frac{d}{dx}[\frac{e^x}{4}-x]\)
Since the derivative of a sum/difference is the sum/difference of the derivatives, we can rewrite the expression:
\(y'(x) = \frac{d}{dx}[\frac{e^x}{4}]-\frac{d}{dx}[x]\)
Now, find the derivatives of each term:
\(y'(x)=\frac{1}{4}e^x - 1\)
02
Evaluate the derivative at \(x=a\)
Now, we need to find the derivative at \(x=a=0\). Substitute \(x=0\) into the expression we found:
\(y'(0)=\frac{1}{4}e^0-1\)
We know that \(e^0 = 1\), so we have:
\(y'(0)=\frac{1}{4}-1\)
After simplifying,
\(y'(0)=-\frac{3}{4}\)
03
Find the point on the curve at \(x=a\)
To find the point on the curve where \(x=a=0\), substitute the value of \(a\) into the original function \(y(x)=\frac{e^x}{4}-x\):
\(y(0)=\frac{e^0}{4}-0\)
Since \(e^0=1\), we have:
\(y(0)=\frac{1}{4}\)
So, the point on the curve is \((0,\frac{1}{4})\).
04
Find the equation of the tangent line
We know the slope of the tangent line from step 2, which is \(-\frac{3}{4}\), and we have the point \((0, \frac{1}{4})\) on the curve from step 3. Now we can use the point-slope form of a line to find the equation of the tangent line:
\(y-y_1=m(x-x_1)\)
Substitute the values:
\(y-\frac{1}{4}=-\frac{3}{4}(x-0)\)
Then, simplify the equation:
\(y=\frac{1}{4}-\frac{3}{4}x\)
The equation of the tangent line at \(x=a=0\) is \(y=\frac{1}{4}-\frac{3}{4}x\).
To graph the curve and the tangent line, use a graphing utility like Desmos or a graphing calculator. Enter the function \(y(x)=\frac{e^x}{4}-x\) and the tangent line equation \(y=\frac{1}{4}-\frac{3}{4}x\). You will see the curve and the tangent line on the same set of axes.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative Calculation
In calculus, the derivative is a core concept used to determine the rate of change of a function. When we find the derivative of a function like \(y(x) = \frac{e^x}{4} - x\), it allows us to understand how the function's output changes with respect to changes in its input. For \(y(x)\), we apply derivative rules:
- The derivative of \(e^x\) is \(e^x\).
- For a constant multiplied by a function, such as \(\frac{e^x}{4}\), the derivative is \(\frac{1}{4} \cdot e^x\).
- The derivative of \(x\) is 1.
Point-Slope Form
The point-slope form is a convenient tool for writing the equation of a line when we know a point on the line and its slope. Recall the point-slope form of a line is given as:\[ y - y_1 = m(x - x_1) \]In this formula:
- \((x_1, y_1)\) is a point on the line.
- \(m\) is the slope of the line.
Graphing Functions
Graphing is a crucial skill to visualize and understand the behavior of functions. For this exercise, you need to graph the function \(y(x) = \frac{e^x}{4} - x\) along with its tangent line \(y = \frac{1}{4} - \frac{3}{4}x\). Here's how you can approach graphing these functions:
- Identify critical points like intersections and turning points, which can be derived from the derivative.
- Plot the original function using the exponential nature of \(e^x\), observing its shape as it approaches infinity.
- Plot the tangent line using the known point \((0, \frac{1}{4})\) and the slope \(-\frac{3}{4}\).
Exponential Functions
Exponential functions are a type of function where the variable appears in the exponent, such as \(e^x\). These functions are pervasive in various mathematical models due to their growth properties. In the context of our function \(y(x) = \frac{e^x}{4} - x\), the term \(\frac{e^x}{4}\) represents an exponential behavior modified by a scaling factor.
- Exponential functions grow rapidly, making them incredibly useful for modeling growth processes, like population growth or radioactive decay.
- In the function \(y(x)\), \(e^x\) contributes to the increasing sequence, while the linear term \(-x\) offsets this growth somewhat.
- This balancing act is what gives the function its unique shape, and understanding this dynamic is essential when anticipating how such functions behave.