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Understanding Function Properties: Graphs of Equations & Functions, Study notes of Calculus

The use of graphs to determine if an equation represents a function, and discusses how to extract valuable information such as intercepts, domain, range, and symmetry from the graphs. It includes examples and instructions on how to find intercepts algebraically and test for symmetry.

What you will learn

  • How do we find the intercepts of an equation using the graph?
  • How can we use the graph of an equation to determine if it is a function?
  • What information can be obtained from the graph of a function?

Typology: Study notes

2021/2022

Uploaded on 09/27/2022

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2.1/3.2 Graphs of Equations and Functions
How do we use the graph of an equation to see if it is a function?
Vertical line test
Ex.
𝑦 = 𝑥 𝑓(𝑥) = 𝑥 𝑥𝑦 = 1 𝑓(𝑥) =
Not a function because f(1)=1 and -1.
*Functions work like the graphs if the function value f(x) is your y.
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How do we use the graph of an equation to see if it is a function?

Vertical line test

Ex. 𝑦 = 𝑥ଷ^ 𝑓(𝑥) = 𝑥ଷ^ 𝑥𝑦 = 1 𝑓(𝑥) = ଵ ௫ Not a function because f(1)=1 and -1. *Functions work like the graphs if the function value f(x) is your y.

Information from Graphs

- Values at certain inputs like or

- Which inputs give positive (or negative) outputs

- Domain

- Range

- Intercepts

- Symmetry

Intercepts

Where an equation crosses the x- or y- axis

What values are on the x- and y-axis? What are their equations? x-axis: y-axis:

Then to find the intercepts algebraically (without graphs), we set y=0 for the x-

intercepts and set x=0 for the y-intercepts.

Ex. 2 𝑥 + 3𝑦 = 6

x-int: y-int:

Test for symmetry:

1. With respect to the x-axis

Set y equal to –y.

2. With respect to the y-axis

Set x equal to –x.

3. With respect to the origin

Symmetry about x- and y-axis

Ex. 2 𝑥 + 3𝑦 = 6 Ex. 9 𝑥ଶ^ + 4𝑦 = 36

Not symmetric y-axis symmetric

Ex. 𝑦 = 𝑥ଷ^ − 27

y-axis symmetric

NOTICE: Functions cannot be x-axis symmetric. Why? Vertical line test

If we have the graphs, we can get all this information directly! Ex. Let f be the function whose graph is shown. (a) What are f(1), f(0), and f(4)?

(b) What is the domain of f?

[-4,4]

(c) What is the range of f? (d) List the intercepts.

[-3,2] x: (-3,0), (0,0), (3,0)

y: (0,0)

(e) For what values of x does f (x) = – 3? (f) For what values of x is f (x) > 0?

4 [-4,-3) and (0,3)

(g) How many times does the line y = – 1 intersect the graph? 3