Let's now plot the graph of y=\tan x, with x in radians.

First, let's create a table for some of the values that we know:

x -\dfrac\pi 2 -\dfrac\pi 3 -\dfrac\pi 4 -\dfrac{\pi} 6 0 \dfrac{\pi} 6 \dfrac{\pi} 4 \dfrac{\pi} 3 \dfrac\pi 2
\tan x \text{undefined} -\sqrt{3} -1 -\dfrac{\sqrt{3}}{3} 0 \dfrac{\sqrt{3}}{3} 1 \sqrt 3 \text{undefined}

Now, let's plot these points to estimate the graph of y=\tan x.

If we inspect the unit circle carefully, we see that the function y=\tan x repeats itself every \pi radians. Therefore, we can extend our plot using this periodicity property:

Some key characteristics of the graph of y=\tan x are as follows:

  • The domain of the function is almost x\in (-\infty ,\infty) except for the points where the function is undefined, namely x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots

  • The range of the function is y\in (-\infty, \infty).

  • The period of the function is \pi.

  • There is no minimum or maximum value.

  • The zeros occur at x=0,\pm\pi,\pm2\pi,\dots

  • The graph has vertical asymptotes at the points not in the domain: x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots. At each asymptote, the graph tends to \infty from the left and -\infty from the right.

FLAG

Which of the following plots is the graph of y=\tan(x)?

EXPLANATION

Let's recall some of the basic properties of y=\tan x\mathbin{:}

  • The domain of the function is almost x\in (-\infty ,\infty) except for the points where the function is undefined, namely x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots

  • The range of the function is y\in (-\infty, \infty).

  • The period of the function is \pi.

  • There is no minimum or maximum value.

  • The zeros occur at x=0,\pm\pi,\pm2\pi,\dots

  • The graph has vertical asymptotes at the points not in the domain: x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots. At each asymptote, the graph tends to \infty from the left and -\infty from the right.

Of the given plots, the only one that has all of these properties is III.

FLAG

Which of the following plots is the graph of $y=\tan(x)?$

a
b
c
d
e

Which of the following plots is the graph of $y=\tan(x)?$

a
b
c
d
e

Which of the following x -values is not in the domain of y=\tan x? 0, \quad \dfrac{\pi}{2}, \quad \dfrac{\pi}{3}, \quad \dfrac{\pi}{4}

EXPLANATION

Let's recall the graph of y=\tan x.

The domain of the function contains all real numbers except for x= \pm\dfrac{\pi}{2}, \pm\dfrac{3\pi}{2},\dots

Of the given values, the only one that is not in the domain is x=\dfrac{\pi}{2}.

FLAG

Which of the following $x$-values is in the domain of $y=\tan x?$

a
$\dfrac{\pi}{2}$
b
$-\dfrac{\pi}{4}$
c
$\dfrac{-3\pi}{2}$
d
$\dfrac{3\pi}{2}$
e
$\dfrac{5\pi}{2}$

Which of the following is a zero of $y=\tan x?$

a
$x=\dfrac{3\pi}{2}$
b
$x=\pi$
c
$x=\dfrac{\pi}{2}$
d
$x=\dfrac{3\pi}{4}$
e
$x=\dfrac{5\pi}{4}$

The cotangent is the reciprocal of the tangent: \cot x = \dfrac{1}{\tan x}.

To plot the graph of y=\cot x, with x in radians, we create a table with some known values:

x 0 \dfrac{\pi}{6} \dfrac{\pi} 4 \dfrac{\pi} 3 \dfrac\pi 2 \dfrac{2\pi} 3 \dfrac{3\pi} 4 \dfrac{5\pi}{6} \pi
\tan x 0 \dfrac{\sqrt{3}}{3} 1 \sqrt{3} \text{undef.} -\sqrt{3} -1 -\dfrac{\sqrt{3}}{3} 0
\cot x \text{undef.} \sqrt{3} 1 \dfrac{\sqrt{3}}{3} 0 -\dfrac{\sqrt{3}}{3} -1 -\sqrt{3} \text{undef.}

Plotting these points gives the following graph:

Notice that:

  • a zero on the graph of y=\tan x corresponds to a vertical asymptote on the graph of y=\cot x, and

  • a vertical asymptote on the graph of y=\tan x corresponds to a zero on the graph of y=\cot x.

The cotangent inherits its periodicity from the tangent, so the period of the cotangent is \pi. Using this periodicity property, we can extend our plot of the cotangent function:

Some key characteristics of the function y=\cot x are:

  • The domain is all real numbers except at the integer multiples of \pi, namely x= 0,\pm\pi,\pm 2\pi,\dots

  • The range of the function is y\in (-\infty, \infty).

  • The period of the function is \pi.

  • There is no minimum or maximum value.

  • The zeros occur at x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots

  • The graph has vertical asymptotes at the points that are not in the domain: x=0, \pm\pi,\pm 2\pi,\dots, and at each asymptote, the graph tends to -\infty from the left and \infty from the right.

FLAG

Which of the following plots is the graph of y=\cot x?

EXPLANATION

Let's recall some of the basic properties of y=\cot x\mathbin{:}

  • The domain is all real numbers except at the integer multiples of \pi : x= 0,\pm\pi,\pm 2\pi,\dots

  • The range of the function is y\in (-\infty, \infty).

  • The period of the function is \pi.

  • There is no minimum or maximum value.

  • The zeros occur at x=\pm\dfrac{\pi}{2},\pm\dfrac{3\pi}{2},\dots

  • The graph has vertical asymptotes at the points that are not in the domain: x=0, \pm\pi,\pm 2\pi,\dots, and at each asymptote, the graph tends to -\infty from the left and \infty from the right.

Of the given plots, the only one that has all of these properties is II.

FLAG

Which of the following plots is the graph of $y=\cot x?$

a
b
c
d
e

Which of the following plots is the graph of $y=\cot x?$

a
b
c
d
e

Which of the following is the equation of a vertical asymptote of the function y=\cot x? x=\dfrac{\pi}{2}, \quad x=2\pi, \quad x=-\dfrac{3\pi}{2}, \quad x=\dfrac{5\pi}{4}

EXPLANATION

Let's recall the graph of y=\cot x.

The graph has vertical asymptotes at the points that are not in the domain:

\qquad x=0, \pm\pi,\pm 2\pi,\dots

At each asymptote, the graph tends to -\infty from the left and \infty from the right.

Of the given equations, the only one that corresponds to an asymptote of the function is x=2\pi.

FLAG

Which of the following $x$-values is in the domain of $y = \cot x?$

a
$\pi$
b
$-5\pi$
c
$\dfrac{\pi}{2}$
d
$-4\pi$
e
$2\pi$

Which of the following is a zero of $y=\cot x?$

a
$x=\dfrac{3\pi}{4}$
b
$x=\dfrac{3\pi}{2}$
c
$x=\dfrac{2\pi}{3}$
d
$x=\dfrac{\pi}{3}$
e
$x=-\dfrac{\pi}{3}$
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