Graphing Trigonometric Functions

Certainly, the best way to understand the behavior of trigonometric functions is to create a visual representation of their graphs on the coordinate plane. This helps us to identify their key features and to analyze the impact of these features on the appearance of each graph. However, do you know what steps to follow to graph trigonometric functions and their reciprocal functions? If your answer is no, then do not worry, as we will guide you through the process.

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Graphing Trigonometric Functions Graphing Trigonometric Functions

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    In this article, we will define what graphs of trigonometric functions are, discuss their key features, and we will show you how to graph trigonometric functions and their reciprocal functions using practical examples.

    Graphs of trigonometric functions are graphical representations of functions or ratios defined based on the sides and the angles of a right triangle. These include the functions sine (sin), cosine (cos), tangent (tan), and their corresponding reciprocal functions cosecant (csc), secant (sec) and cotangent (cot).

    What are the key features of trigonometric functions graphs?

    Before we go through the process to graph trigonometric functions, we need to identify some key features about them:

    Amplitude

    The amplitude of trigonometric functions refers to the vertical stretch factor, which you can calculate as the absolute value of half the difference between its maximum value and its minimum value.

    The amplitude of the functions y=sin θ and y=cos θ is 1-(-1)2=1.

    For functions in the form y=a sin bθ, or y=a cos bθ, the amplitude equals the absolute value of a.

    Amplitude=a

    If you have the trigonometric function y=2 sinθ, then the amplitude of the function is 2.

    The tangent functions graph has no amplitude, as it does not have a minimum or maximum value.

    Period

    The period of trigonometric functions is the distance along the x-axis from where the pattern starts, to the point where it starts again.

    The period of sine and cosine is 2π or 360º.

    For functions in the form y=a sin bθ, or y=a cos bθ, b is known as the horizontal stretch factor, and you can calculate the period as follows:

    Period=2πb or 360°b

    For functions in the form y=a tan bθ, the period is calculated like this:

    Period=πb or 180°b

    Find the period of the following trigonometric functions:

    • y=cos π2θ
    Period=2πb=2ππ2=2ππ2=4ππ=4
    • y=tan 13θ
    Period=πb=π13=π13=3π

    Domain and range

    The domain and range of the main trigonometric functions are as follows:

    Trigonometric functionDomainRange
    SineAll real numbers-1y1
    CosineAll real numbers-1y1
    TangentAll real numbers, apart from2, where n=±1, ±3, ±5, ...All real numbers
    CosecantAll real numbers, apart from nπ, where n=0, ±1, ±2, ±3, ...(-, -1] [1, )
    SecantAll real numbers, apart from 2, where n=±1, ±3, ±5, ...(-, -1] [1, )
    CotangentAll real numbers, apart from nπ, where n=0, ±1, ±2, ±3, ...All real numbers

    Remember that all trigonometric functions are periodic, because their values repeat over and over again after a specific period.

    How to graph trigonometric functions?

    To graph the trigonometric functions you can follow these steps:

    • If the trigonometric function is in the form y=a sin bθ, y=a cos bθ, or y=a tan bθ, then identify the values of a and b, and work out the values of the amplitude and the period as explained above.

    • Create a table of ordered pairs for the points that you will include in the graph. The first value in the ordered pairs will correspond to the value of the angle θ, and the values of y will correspond to the value of the trigonometric function for the angle θ, for example, sin θ, so the ordered pair will be (θ, sin θ). The values of θ can be either in degrees or radians.

    You can use the unit circle to help you work out the values of sine and cosine for the most commonly used angles. Please read about Trigonometric Functions, if you need to recap how to do this.

    • Plot a few points on the coordinate plane to complete at least one period of the trigonometric function.

    • Connect the points with a smooth and continuous curve.

    Sine graph

    Sine is the ratio of the length of the opposite side of the right triangle over the length of the hypotenuse.

    The graph for a sine function y=sin θ looks like this:

    Graphing Trigonometric Functions Sine graph StudySmarterSine graph, Marilú García De Taylor - StudySmarter Originals

    From this graph we can observe the key features of the sine function:

    • The graph repeats every 2π radians or 360°.

    • The minimum value for sine is -1.

    • The maximum value for sine is 1.

    • This means that the amplitude of the graph is 1 and its period is 2π (or 360°).

    • The graph crosses the x-axis at 0 and every π radians before and after that.

    • The sine function reaches its maximum value at π/2 and every 2π before and after that.

    • The sine function reaches its minimum value at 3π/2 and every 2π before and after that.

    Graph the trigonometric function y=4 sin 2θ

    • Identify the values of a and b

    a=4, b=2

    • Calculate the amplitude and period:

    Amplitude=a=4=4Period=2πb=2π2=2π2=π

    • Table of ordered pairs:
    θy=4 sin 2θ
    00
    π44
    π20
    3π4-4
    π0
    • Plot the points and connect them with a smooth and continuous curve:

    Graphing Trigonometric Functions Sine graph example StudySmarterSine graph example, Marilú García De Taylor - StudySmarter Originals

    Cosine graph

    Cosine is the ratio of the length of the adjacent side of the right triangle over the length of the hypotenuse.

    The graph for the cosine function y=cos θlooks exactly like the sine graph, except that it is shifted to the left by π/2 radians, as shown below.

    Graphing Trigonometric Functions Cosine graph StudySmarterCosine graph, Marilú García De Taylor - StudySmarter Originals

    By observing this graph, we can determine the key features of the cosine function:

    • The graph repeats every 2π radians or 360°.

    • The minimum value for cosine is -1.

    • The maximum value for cosine is 1.

    • This means that the amplitude of the graph is 1 and its period is 2π (or 360°).

    • The graph crosses the x-axis at π/2 and every π radians before and after that.

    • The cosine function reaches its maximum value at 0 and every 2π before and after that.

    • The cosine function reaches its minimum value at π and every 2π before and after that.

    Graph the trigonometric function y=2 cos 12θ

    • Identify the values of a and b:
    a=2, b=12
    • Calculate the amplitude and period:
    Amplitude=a=2=2Period=2πb=2π12=2π12=4π
    • Table of ordered pairs:

    θ

    y=2 cos 12θ
    02
    π0
    2π-2
    3π0
    4π2
    • Plot the points and connect them with a smooth and continuous curve:

    Graphing Trigonometric Functions Cosine graph example StudySmarterCosine graph example, Marilú García De Taylor - StudySmarter Originals

    Tangent graph

    Tangent is the ratio of the length of the opposite side of the right triangle over the length of the adjacent side.

    The graph of the tangent function y=tan θ, however, looks a bit different than the cosine and sine functions. It is not a wave but rather a discontinuous function, with asymptotes:

    Graphing Trigonometric Functions Tangent graph StudySmarterTangent graph, Marilú García De Taylor - StudySmarter Originals

    By observing this graph, we can determine the key features of the tangent function:

    • The graph repeats every π radians or 180°.

    • No minimum value.

    • No maximum value.

    • This means that the tangent function has no amplitude and its period is π (or 180°).

    • The graph crosses the x-axis at 0 and every π radians before and after that.

    • The tangent graph has asymptotes, which are values where the function is undefined.

    • These asymptotes are at π/2 and every π before and after that.

    The tangent of an angle can also be found with this formula:

    tan θ=sin θcos θ

    Graph the trigonometric function y=34 tan θ

    • Identify the values of a and b:
    a=34, b=1

    • Calculate the amplitude and period:
    Tangent functions have no amplitude. Period=πb=π1=π1=π
    • Table of ordered pairs:
      θy=34 tan θ
      -π2undefined(asymptote)
      -π4-34
      00
      π434
      π2undefined(asymptote)
    • Plot the points and connect them:

    Graphing Trigonometric Functions Tangent graph example StudySmarterTangent graph example, Marilú García De Taylor - StudySmarter Originals

    What are the graphs of the reciprocal trigonometric functions?

    Each trigonometric function has a corresponding reciprocal function:

    • Cosecant is the reciprocal of sine.
    • Secant is the reciprocal of cosine.
    • Cotangent is the reciprocal of tangent.

    To graph the reciprocal trigonometric functions you can proceed as follows:

    Cosecant graph

    The graph of the cosecant function y=csc θ can be obtained like this:

    • Graph the corresponding sine function first, to use it as a guide.
    • Draw vertical asymptotes in all the points where the sine function intercepts the x-axis.
    • The cosecant graph will touch the sine function at its maximum and minimum value. From those points, draw the reflection of the sine function, which approaches but never touches the vertical asymptotes and extends to positive and negative infinity.

    Graphing Trigonometric Functions Cosecant graph StudySmarterCosecant graph, Marilú García De Taylor - StudySmarter Originals

    The cosecant function graph has the same period as the sine graph, which is 2π or 360°, and it has no amplitude.

    Graph the reciprocal trigonometric function y=2 csc θ

    • a=2, b=1
    • No amplitude
    • Period=2πb=2π1=2π1=2π

    Graphing Trigonometric Functions Cosecant graph example StudySmarterCosecant graph example, Marilú García De Taylor - StudySmarter Originals

    Secant graph

    To graph the secant function y=sec θ you can follow the same steps as before, but using the corresponding cosine function as a guide. The secant graph looks like this:

    Graphing Trigonometric Functions Secant graph StudySmarterSecant graph, Marilú García De Taylor - StudySmarter Originals

    The secant function graph has the same period as the cosine graph, which is 2π or 360°, and it also has no amplitude.

    Graph the reciprocal trigonometric function y=12 sec 2θ

    • a=12, b=2
    • No amplitude
    • Period=2πb=2π2=2π2=π

    Graphing Trigonometric Functions Secant graph example StudySmarterSecant graph example, Marilú García De Taylor - StudySmarter Originals

    Cotangent graph

    The cotangent graph is very similar to the graph of tangent, but instead of being an increasing function, cotangent is a decreasing function. The cotangent graph will have asymptotes in all the points where the tangent function intercepts the x-axis.

    Graphing Trigonometric Functions Cotangent graph StudySmarterCotangent graph, Marilú García De Taylor - StudySmarter Originals

    The period of the cotangent graph is the same as the period of the tangent graph, π radians or 180°, and it also has no amplitude.

    Graph the reciprocal trigonometric function y=3 cot θ

    • a=3, b=1
    • No amplitude
    • Period=πb=π1=π1=π

    Graphing Trigonometric Functions Cotangent graph example StudySmarterCotangent graph example, Marilú García De Taylor - StudySmarter Originals

    What are the graphs of the inverse trigonometric functions?

    The inverse trigonometric functions refer to the arcsine, arccosine and arctangent functions, which can also be written as Sin-1, Cos-1 and Tan-1. These functions do the opposite of the sine, cosine and tangent functions, which means that they give back an angle when we plug a sin, cos or tan value into them.

    Remember that the inverse of a function is obtained by swapping x and y, that is, x becomes y and y becomes x.

    The inverse of y=sin x is x=sin y, and you can see its graph below:

    Graphing Trigonometric Functions Inverse of sine graph StudySmarterInverse of sine graph, Marilú García De Taylor - StudySmarter Originals

    However, in order to make the inverses of trigonometric functions become functions, we need to restrict their domain. Otherwise, the inverses are not functions because they do not pass the vertical line test. The values in the restricted domains of the trigonometric functions are known as principal values, and to identify that these functions have a restricted domain, we use capital letters:

    Trigonometric functionRestricted domain notationPrincipal values
    Siney=Sin x-π2xπ2
    Cosiney=Cos x0xπ
    Tangenty=Tan x-π2<x<π2

    Arcsine graph

    Arcsine is the inverse of the sine function. The inverse of y=Sin x is defined as x=Sin-1 y or x=Arcsin y. The domain of the arcsine function will be all real numbers from -1 to 1, and its range is the set of angle measures from -π2yπ2. The graph of the arcsine function looks like this:

    Graphing Trigonometric Functions Arcsine graph StudySmarterArcsine graph, Marilú García De Taylor - StudySmarter Originals

    Arccosine graph

    Arccosine is the inverse of the cosine function. The inverse of y=Cos x is defined as x=Cos-1 y or x=Arccos y. The domain of the arccosine function will be also all real numbers from -1 to 1, and its range is the set of angle measures from 0yπ. The graph of the arccosine function is shown below:

    Graphing Trigonometric Functions Arccosine graph StudySmarterArccosine graph, Marilú García De Taylor - StudySmarter Originals

    Arctangent graph

    Arctangent is the inverse of the tangent function. The inverse of y=Tan x is defined asx=Tan-1 y or x=Arctan y. The domain of the arctangent function will be all real numbers, and its range is the set of angle measures between -π2<y<π2. The arctangent graph looks like this:

    Graphing Trigonometric Functions Arctangent graph StudySmarterArctangent graph, Marilú García De Taylor - StudySmarter Originals

    If we graph all the inverse functions together, they look like this:

    Graphing Trigonometric Functions Arcsine, arccosine, and arctangent graphs StudySmarterArcsine, Arccosine, and Arctangent graphs together, Marilú García De Taylor - StudySmarter Originals

    Please refer to the Inverse Trigonometric Functions article to learn more about this topic.

    Graphing trigonometric functions - Key takeaways

    • Graphs of trigonometric functions are graphical representations of functions or ratios defined based on the sides and the angles of a right triangle.
    • The key features of trigonometric functions are: amplitude, period, domain and range.
    • The amplitude of trigonometric functions refers to the vertical stretch factor, which you can calculate as the absolute value of half the difference between its maximum value and its minimum value.
    • The period of trigonometric functions is the distance along the x-axis from where the pattern starts, to the point where it starts again.
    • Each trigonometric function has a corresponding reciprocal function. Cosecant is the reciprocal of sine, secant is the reciprocal of cosine, and cotangent is the reciprocal of tangent.
    • The inverse trigonometric functions arcsine, arccosine and arctangent, do the opposite of the sine, cosine and tangent functions, which means that they give back an angle when we plug a sin, cos or tan value into them.
    Graphing Trigonometric Functions Graphing Trigonometric Functions
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    Frequently Asked Questions about Graphing Trigonometric Functions

    What are graphs of trigonometric functions?

    Graphs of trigonometric functions are graphical representations of functions or ratios defined based on the sides and the angles of a right triangle. These include the functions sine (sin), cosine (cos), tangent (tan), and their corresponding reciprocal functions cosecant (csc), secant (sec) and cotangent (cot).

    What are the rules when graphing trigonometric functions?

    • Identify its key features: amplitude (vertical stretch factor) and period.
    • Plot a few points on the coordinate plane to complete one period of the function.
    • Connect the points with a smooth and continuous curve.
    • Continue the graph if required, by repeating the pattern after each period.


    How to graph trigonometric functions?

    To graph the trigonometric functions you can follow these steps:

    • If the trigonometric function is in the form y = a sin bθ, y = a cos bθ, or y = a tan bθ, then identify the values of a and b, and work out the values of the amplitude and the period.        
    • Create a table of ordered pairs for the points to include in the graph. The first value in the ordered pairs will correspond to the value of the angle θ, and the values of y will correspond to the value of the trigonometric function for the angle θ, for example, sin θ, so the ordered pair will be (θ, sin θ). The values of θ can be either in degrees or radians.
    • Plot a few points on the coordinate plane to complete at least one period of the trigonometric function. 
    • Connect the points with a smooth and continuous curve.


    What is an example of trigonometric function graphs?

    The graph for a sine function has the following characteristics:

    • It has a wave shape.
    • The graph repeats every 2π radians or 360°.
    • The minimum value for sine is -1.
    • The maximum value for sine is 1.
    • This means that the amplitude of the graph is 1 and its period is 2π (or 360°).
    • The graph crosses the x-axis at 0 and every π radians before and after that. 

            


    How to draw graphs of inverse trigonometric functions?

    To draw graphs of inverse trigonometric functions proceed as follows:

    • Restrict the domain of the trigonometric function to its principal values.
    • Work out the domain and range. The domain of the inverse will be the range of its corresponding trigonometric function, and the range of the inverse will be the restricted domain of its trigonometric function.
    • Plot a few points and connect them with a smooth and continuous curve.

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