Chapter 3: Problem 27
Find the equation of the line tangent to the graph of \(\tan x\) at the point where (a) \(x=0\) (b) \(x=\pi / 4\) (c) \(x=-\pi / 4\)
Short Answer
Expert verified
(a) y = x, (b) y = 2x - \pi/2 + 1, (c) y = 2x + \pi/2 - 1.
Step by step solution
01
Identify the function and the derivative
The function given is the tangent function, denoted as \( y = \tan x \). To find the equation of the tangent line, we first need the derivative of \( \tan x \), which is \( \sec^2 x \). The derivative \( \sec^2 x \) will give us the slope of the tangent line at any point \( x \).
02
Calculate the slope at x = 0
Substitute \( x = 0 \) into the derivative \( \sec^2 x \):\[ \sec^2 0 = 1^2 = 1 \]Thus, the slope of the tangent at \( x = 0 \) is 1.
03
Determine the point on the curve for x = 0
Substitute \( x = 0 \) into the function \( y = \tan x \):\[ y = \tan 0 = 0 \]This gives the point \( (0,0) \) on the curve.
04
Find the tangent line equation at x = 0
The equation of the tangent line is \( y = mx + b \), where \( m \) is the slope and \( b \) is the y-intercept. We have \( m = 1 \) and point \( (0, 0) \). Substitute this into the line equation:\[ y = 1(x) + 0 \]Therefore, the tangent line at \( x = 0 \) is \( y = x \).
05
Calculate the slope at x = \( \pi / 4 \)
Substitute \( x = \pi/4 \) into the derivative:\[ \sec^2 (\pi/4) = (\sqrt{2})^2 = 2 \]Thus, the slope of the tangent at \( x = \pi/4 \) is 2.
06
Determine the point on the curve for x = \( \pi / 4 \)
Substitute \( x = \pi/4 \) into the function:\[ y = \tan(\pi/4) = 1 \]So, the point on the curve is \( (\pi/4, 1) \).
07
Find the tangent line equation at x = \( \pi / 4 \)
Using point-slope form \( y - y_1 = m(x - x_1) \) where \( m = 2 \) and \( (x_1, y_1) = (\pi/4, 1) \), we have:\[ y - 1 = 2(x - \pi/4) \]Simplify to find the tangent equation:\[ y = 2x - \pi/2 + 1 \]\[ y = 2x - \pi/2 + 1 \] is the tangent line at \( x = \pi/4 \).
08
Calculate the slope at x = \( -\pi / 4 \)
In the same way, substitute \( x = -\pi/4 \) into the derivative:\[ \sec^2 (-\pi/4) = (\sqrt{2})^2 = 2 \]Thus, the slope of the tangent at \( x = -\pi/4 \) is 2.
09
Determine the point on the curve for x = \( -\pi / 4 \)
Substitute \( x = -\pi/4 \) into the function:\[ y = \tan(-\pi/4) = -1 \]So, the point on the curve is \( (-\pi/4, -1) \).
10
Find the tangent line equation at x = \( -\pi / 4 \)
Using point-slope form with \( m = 2 \) and \( (x_1, y_1) = (-\pi/4, -1) \), we write:\[ y + 1 = 2(x + \pi/4) \]Simplify to find the tangent equation:\[ y = 2x + \pi/2 - 1 \]Thus, the tangent line at \( x = -\pi/4 \) is \( y = 2x + \pi/2 - 1 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative of Trigonometric Functions
Trigonometric functions are a fundamental part of calculus and mathematics. Understanding their derivatives helps in finding slopes of tangent lines. The function in our exercise is the tangent function, denoted as \( y = \tan x \). The derivative of the tangent function, which is \( \sec^2 x \), plays a vital role in our solution. To find this derivative, consider how each trigonometric function has a unique derivative. For example:
\( \sin x \) differentiates to \( \cos x \)
\( \cos x \) differentiates to \( -\sin x \)
When you differentiate \( \tan x \), remember that it can be expressed as a quotient, \( \frac{\sin x}{\cos x} \). Applying the quotient rule, the derivative becomes \( \sec^2 x \). This derivative, \( \sec^2 x \), tells us the slope of the tangent line at any point \( x \). By substituting specific values of \( x \), we find the slope at desired points, which are crucial for forming the equation of the tangent line.
\( \sin x \) differentiates to \( \cos x \)
\( \cos x \) differentiates to \( -\sin x \)
When you differentiate \( \tan x \), remember that it can be expressed as a quotient, \( \frac{\sin x}{\cos x} \). Applying the quotient rule, the derivative becomes \( \sec^2 x \). This derivative, \( \sec^2 x \), tells us the slope of the tangent line at any point \( x \). By substituting specific values of \( x \), we find the slope at desired points, which are crucial for forming the equation of the tangent line.
Equation of a Line
The equation of a line can be represented in different forms, the most common being the slope-intercept form, \( y = mx + b \), where \( m \) is the slope and \( b \) is the y-intercept. In the context of tangent lines, the point-slope form is very useful:
\[ y - y_1 = m(x - x_1) \]
Where \( (x_1, y_1) \) is a point on the line and \( m \) is the slope.
To find the tangent line of a given function at a specified point, you perform a few straightforward steps:
\[ y - y_1 = m(x - x_1) \]
Where \( (x_1, y_1) \) is a point on the line and \( m \) is the slope.
To find the tangent line of a given function at a specified point, you perform a few straightforward steps:
- First, determine the slope \( m \) using the derivative of the function.
- Next, identify a specific point on the curve where the tangent touches. This values helps in calculating \((x_1, y_1)\).
- Finally, plug these values into the point-slope form and simplify to get the equation in slope-intercept form if needed.
Trigonometric Functions
Trigonometric functions, like sine, cosine, and tangent, are essential in describing phenomena involving angles and periodicity. The tangent function, \( \tan x \), is defined as the ratio of sine and cosine, \( \frac{\sin x}{\cos x} \), and is important in trigonometry due to its unique properties and behavior. At various angles such as \( x = 0 \), \( \pi/4 \), or \( -\pi/4 \), the tangent provides distinct values that help in many applications, including determining tangent lines.
When working with these trigonometric functions, it's vital to remember:
When working with these trigonometric functions, it's vital to remember:
- Tangent is undefined at angles where cosine is zero, like \( \frac{\pi}{2} \).
- The periodicity of tangent is \( \pi \), meaning it repeats every \( \pi \) radians.
- For certain key angles, we can easily determine tangent values without computation, such as \( \tan(0) = 0 \), \( \tan(\pi/4) = 1 \), and \( \tan(-\pi/4) = -1 \).