How to graph Functions

Warm Up Lesson Presentation Lesson Quiz 4-4 Graphing Functions Holt Algebra 1

Warm Up Solve each equation for y. 1. 2 x + y = 3 2. – x + 3 y = –6 3. 4 x – 2 y = 8 4. Generate ordered pairs for using x = – 4, – 2, 0, 2 and 4. y = –2 x + 3 y = 2 x – 4 (–4, –1), (–2, 0), (0, 1), (2, 2), (4, 3)

Graph functions given a limited domain. Graph functions given a domain of all real numbers. Objectives

Scientists can use a function to make conclusions about the rising sea level. Sea level is rising at an approximate rate of 2.5 millimeters per year. If this rate continues, the function y = 2.5 x can describe how many millimeters y sea level will rise in the next x years. You can graph a function by finding ordered pairs that satisfy the function.

Example 1A: Graphing Functions Given a Domain Graph the function for the given domain. x – 3 y = –6; D: {–3, 0, 3, 6} Step 1 Solve for y since you are given values of the domain, or x . – 3 y = – x – 6 Subtract x from both sides. Since y is multiplied by –3, divide both sides by –3. Simplify. x – 3 y = –6 – x – x

Example 1A Continued Step 2 Substitute the given value of the domain for x and find values of y. x ( x , y ) Graph the function for the given domain. – 3 (–3, 1) 0 (0, 2) 3 (3, 3) 6 (6, 4)

Step 3 Graph the ordered pairs. Example 1A Continued Graph the function for the given domain. • • • • y x

Graph the function for the given domain. f ( x ) = x 2 – 3; D: {–2, –1, 0, 1, 2} Example 1B: Graphing Functions Given a Domain Step 1 Use the given values of the domain to find values of f ( x ). f ( x ) = x 2 – 3 ( x, f ( x )) x – 2 – 1 0 1 2 f ( x ) = ( –2 ) 2 – 3 = 1 f ( x ) = ( –1 ) 2 – 3 = –2 f ( x ) = 0 2 – 3 = –3 f ( x ) = 1 2 – 3 = –2 f ( x ) = 2 2 – 3 = 1 (–2, 1) (–1, –2) (0, –3) (1, –2) (2, 1)

Step 2 Graph the ordered pairs. Graph the function for the given domain. f ( x ) = x 2 – 3; D: {–2, –1, 0, 1, 2} Example 1B Continued • • • • • y x

Check It Out! Example 1a Graph the function for the given domain. – 2 x + y = 3; D: {–5, –3, 1, 4} Step 1 Solve for y since you are given values of the domain, or x . – 2 x + y = 3 y = 2 x + 3 Add 2x to both sides. +2 x +2 x

Check It Out! Example 1a Continued Graph the function for the given domain. – 2 x + y = 3; D: {–5, –3, 1, 4} y = 2 x + 3 x ( x, y ) Step 2 Substitute the given values of the domain for x and find values of y . y = 2( –5 ) + 3 = –7 – 5 (–5, –7) y = 2( 1 ) + 3 = 5 1 (1, 5) y = 2( 4 ) + 3 = 11 4 (4, 11) y = 2( –3 ) + 3 = –3 – 3 (–3, –3)

Step 3 Graph the ordered pairs. Check It Out! Example 1a Continued Graph the function for the given domain. – 2 x + y = 3; D: {–5, –3, 1, 4}

Graph the function for the given domain. f ( x ) = x 2 + 2; D: {–3, –1, 0, 1, 3} Check It Out! Example 1b Step 1 Use the given values of the domain to find the values of f ( x ). f ( x ) = x 2 + 2 x ( x, f ( x )) f ( x ) = ( –3 2 ) + 2= 11 – 3 (–3, 11) f ( x ) = 0 2 + 2= 2 0 (0, 2) f ( x ) = 1 2 + 2=3 1 (1, 3) f ( x ) = ( –1 2 ) + 2= 3 – 1 (–1, 3) 3 f ( x ) = 3 2 + 2=11 (3, 11)

Step 2 Graph the ordered pairs. Graph the function for the given domain. f ( x ) = x 2 + 2; D: {–3, –1, 0, 1, 3} Check It Out! Example 1b

If the domain of a function is all real numbers, any number can be used as an input value. This process will produce an infinite number of ordered pairs that satisfy the function. Therefore, arrowheads are drawn at both “ends” of a smooth line or curve to represent the infinite number of ordered pairs. If a domain is not given, assume that the domain is all real numbers.

Graphing Functions Using a Domain of All Real Numbers Step 1 Use the function to generate ordered pairs by choosing several values for x. Step 2 Step 3 Plot enough points to see a pattern for the graph. Connect the points with a line or smooth curve.

Example 2A: Graphing Functions Graph the function –3 x + 2 = y . – 3( 1 ) + 2 = –1 1 (1, –1) 0 – 3( 0 ) + 2 = 2 (0, 2) Step 1 Choose several values of x and generate ordered pairs. – 1 (–1, 5) – 3( –1 ) + 2 = 5 – 3( 2 ) + 2 = –4 2 (2, –4) 3 – 3( 3 ) + 2 = –7 (3, –7) – 3( –2 ) + 2 = 8 – 2 (–2, 8) ( x, y ) – 3 x + 2 = y x

Step 2 Plot enough points to see a pattern. Example 2A Continued Graph the function –3 x + 2 = y .

Step 3 The ordered pairs appear to form a line. Draw a line through all the points to show all the ordered pairs that satisfy the function. Draw arrowheads on both “ends” of the line. Example 2A Continued Graph the function –3 x + 2 = y .

Example 2B: Graphing Functions g ( x ) = | –2 | + 2= 4 – 2 (–2, 4) g ( x ) = | 1 | + 2= 3 1 (1, 3) 0 g ( x ) = | 0 | + 2= 2 (0, 2) Step 1 Choose several values of x and generate ordered pairs. g ( x ) = | –1 | + 2= 3 – 1 (–1, 3) g ( x ) = | 2 | + 2= 4 2 (2, 4) g ( x ) = | 3 | + 2= 5 3 (3, 5) Graph the function g ( x ) = | x | + 2. ( x , g ( x )) g ( x ) = | x | + 2 x

Step 2 Plot enough points to see a pattern. Example 2B Continued Graph the function g ( x ) = | x | + 2.

Step 3 The ordered pairs appear to form a v-shape. Draw lines through all the points to show all the ordered pairs that satisfy the function. Draw arrowheads on the “ends” of the “v”. Example 2B Continued Graph the function g ( x ) = | x | + 2.

Check If the graph is correct, any point on it should satisfy the function. Choose an ordered pair on the graph that was not in your table. ( 4 , 6 ) is on the graph. Check whether it satisfies g ( x )= | x | + 2. 6 | 4 | + 2 6 4 + 2 6 6  Substitute the values for x and y into the function. Simplify. The ordered pair (4, 6) satisfies the function. Example 2B Continued Graph the function g ( x ) = | x | + 2. g ( x ) = | x | + 2

Check It Out! Example 2a Graph the function f ( x ) = 3 x – 2. f ( x ) = 3( –2 ) – 2 = –8 – 2 (–2, –8) f ( x ) = 3( 1 ) – 2 = 1 1 (1, 1) 0 f ( x ) = 3( 0 ) – 2 = –2 (0, –2) Step 1 Choose several values of x and generate ordered pairs. f ( x ) = 3( –1 ) – 2 = –5 – 1 (–1, –5) f ( x ) = 3( 2 ) – 2 = 4 2 (2, 4) f ( x ) = 3( 3 ) – 2 = 7 3 (3, 7) ( x , f ( x )) f ( x ) = 3 x – 2 x

Step 2 Plot enough points to see a pattern. Check It Out! Example 2a Continued Graph the function f ( x ) = 3 x – 2.

Step 3 The ordered pairs appear to form a line. Draw a line through all the points to show all the ordered pairs that satisfy the function. Draw arrowheads on both “ends” of the line. Check It Out! Example 2a Continued Graph the function f ( x ) = 3 x – 2.

Graph the function y = | x – 1|. y = | – 2 – 1| = 3 – 2 (–2, 3) y = | 1 – 1| = 0 1 (1, 0) 0 y = | 0 – 1| = 1 (0, 1) Step 1 Choose several values of x and generate ordered pairs. y = | –1 – 1| = 2 – 1 (–1, 2) y = | 2 – 1| = 1 2 (2, 1) Check It Out! Example 2b ( x , y ) y = |x – 1 | x

Step 2 Plot enough points to see a pattern. Graph the function y = | x – 1|. Check It Out! Example 2b Continued

Step 3 The ordered pairs appear to form a V-shape. Draw a line through the points to show all the ordered pairs that satisfy the function. Draw arrowheads on both “ends” of the “V”.. Graph the function y = | x – 1|. Check It Out! Example 2b Continued

Check If the graph is correct, any point on the graph should satisfy the function. Choose an ordered pair on the graph that is not in your table. ( 3 , 2 ) is on the graph. Check whether it satisfies y = | x − 1|. 2 | 3 – 1| 2 |2| 2 2  Substitute the values for x and y into the function. Simplify. The ordered pair (3, 2) satisfies the function. Graph the function y = | x – 1|. Check It Out! Example 2b Continued y = | x – 1|

Example 3: Finding Values Using Graphs Use a graph of the function to find the value of f ( x ) when x = –4. Check your answer. Locate –4 on the x -axis. Move up to the graph of the function. Then move right to the y- axis to find the corresponding value of y. f (–4) = 6

 Check Use substitution. Example 3 Continued Substitute the values for x and y into the function. Simplify. The ordered pair (–4, 6) satisfies the function. Use a graph of the function to find the value of f ( x ) when x = –4. Check your answer. f (–4) = 6 6 2 + 4 6 6 6

Check It Out! Example 3 Use the graph of to find the value of x when f ( x ) = 3. Check your answer. Locate 3 on the y- axis. Move right to the graph of the function. Then move down to the x- axis to find the corresponding value of x. f(3) = 3

 Check Use substitution. Substitute the values for x and y into the function. Simplify. The ordered pair (3, 3) satisfies the function. Check It Out! Example 3 Continued Use the graph of to find the value of x when f ( x ) = 3. Check your answer. f(3) = 3 3 1 + 2 3 3 3

Recall that in real-world situations you may have to limit the domain to make answers reasonable. For example, quantities such as time, distance, and number of people can be represented using only nonnegative values. When both the domain and the range are limited to nonnegative values, the function is graphed only in Quadrant I.

Example 4: Problem-Solving Application A mouse can run 3.5 meters per second. The function y = 3.5 x describes the distance in meters the mouse can run in x seconds. Graph the function. Use the graph to estimate how many meters a mouse can run in 2.5 seconds.

Example 4 Continued The answer is a graph that can be used to find the value of y when x is 2.5. List the important information: • The function y = 3.5 x describes how many meters the mouse can run. Understand the Problem 1

Think: What values should I use to graph this function? Both the number of seconds the mouse runs and the distance the mouse runs cannot be negative. Use only nonnegative values for both the domain and the range. The function will be graphed in Quadrant I. Example 4 Continued 2 Make a Plan

Choose several nonnegative values of x to find values of y. Example 4 Continued Solve 3 y = 3.5 x x ( x, y ) y = 3.5( 1 ) = 3.5 1 (1, 3.5) y = 3.5( 2 ) = 7 2 (2, 7) 3 y = 3.5( 3 ) = 10.5 (3, 10.5) y = 3.5( 0 ) = 0 0 (0, 0)

Graph the ordered pairs. Draw a line through the points to show all the ordered pairs that satisfy this function. Use the graph to estimate the y -value when x is 2.5. A mouse can run about 8.75 meters in 2.5 seconds. Example 4 Continued Solve 3

As time increases, the distance traveled also increases, so the graph is reasonable. When x is between 2 and 3, y is between 7 and 10.5. Since 2.5 is between 2 and 3, it is reasonable to estimate y to be 8.75 when x is 2.5. Example 4 Continued Look Back 4

Check It Out! Example 4 The fastest recorded Hawaiian lava flow moved at an average speed of 6 miles per hour. The function y = 6 x describes the distance y the lava moved on average in x hours. Graph the function. Use the graph to estimate how many miles the lava moved after 5.5 hours.

Check It Out! Example 4 Continued The answer is a graph that can be used to find the value of y when x is 5.5. List the important information: • The function y = 6 x describes how many miles the lava can flow. Understand the Problem 1

Think: What values should I use to graph this function? Both the speed of the lava and the number of hours it flows cannot be negative. Use only nonnegative values for both the domain and the range. The function will be graphed in Quadrant I. Check It Out! Example 4 Continued 2 Make a Plan

Choose several nonnegative values of x to find values of y. Check It Out! Example 4 Continued Solve 3 y = 6 x x ( x, y ) y = 6( 1 ) = 6 1 (1, 6) y = 6( 3 ) = 18 3 (3, 18) 5 y = 6( 5 ) = 30 (5, 30)

Draw a line through the points to show all the ordered pairs that satisfy this function. Use the graph to estimate the y -value when x is 5.5. The lava will travel about 32.5 meters in 5.5 seconds. Check It Out! Example 4 Continued Graph the ordered pairs. Solve 3

As the amount of time increases, the distance traveled by the lava also increases, so the graph is reasonable. When x is between 5 and 6, y is between 30 and 36. Since 5.5 is between 5 and 6, it is reasonable to estimate y to be 32.5 when x is 5.5. Check It Out! Example 4 Continued Look Back 4

Lesson Quiz: Part I 1. Graph the function for the given domain. 3 x + y = 4 D: {–1, 0, 1, 2} 2. Graph the function y = | x + 3|.

Lesson Quiz: Part II 3. The function y = 3 x describes the distance (in inches) a giant tortoise walks in x seconds. Graph the function. Use the graph to estimate how many inches the tortoise will walk in 5.5 seconds. About 16.5 in.

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