section 7.5 graphing square root and cube root functions

Section 7.5

Graphing Square root and Cube root

functions

Domain: x 0, Range: y 0 Domain and range: all real numbers

Graphing Radical Functions

You have seen the graphs of y = x and y = x . These are examples of radical functions.

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Domain: x 0, Range: y 0 Domain and range: all real numbers

Graphing Radical Functions

You have seen the graphs of y = x and y = x . These are examples of radical functions.

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In this lesson you will learn to graph functions of the form y = a x – h + k and y = a x – h + k.3

Graphing Radical Functions

GRAPHS OF RADICAL FUNCTIONS

1STEP

Shift the graph h units horizontally and k units vertically.2STEP

To graph y = a x – h + k or y = a x – h + k, follow these steps.3

Sketch the graph of y = a x or y = a x .3

Comparing Two Graphs

SOLUTION

Describe how to obtain the graph of y = x + 1 – 3 from the graph of y = x .

To obtain the graph of y = x + 1 – 3, shift the graph of y = x left 1 unitand down 3 units.

Note that y = x + 1 – 3 = x – (–1) + (–3), so h = –1 and k = –3.

Graphing a Square Root Function

SOLUTION

1

2

So, shift the graph right 2 units and up 1 unit.

The result is a graph that starts at (2, 1) and passes through the point (3, –2).

Graph y = –3 x – 2 + 1.

Note that for y = –3 x – 2 + 1, h = 2 and k = 1.

Sketch the graph of y = –3 x (shown dashed). Notice that it begins at the origin and passes through the point (1, –3).

Graphing a Cube Root Function

SOLUTION

1

2

So, shift the graph left 2 units and down 1 unit.

The result is a graph that passes through the points (–3, –4), (–2, –1), and (–1, 2).

Graph y = 3 x + 2 – 1.3

Sketch the graph of y = 3 x (shown dashed). Notice that it passes through the origin and the points (–1, –3) and (1, 3).

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Note that for y = 3 x + 2 – 1, h = –2 and k = –1.

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Finding Domain and Range

State the domain and range of the functions in the previous examples.

SOLUTION

From the graph of y = –3 x – 2 + 1, you can see that the domain of the function is x 2 and the range of the function is y 1.

Finding Domain and Range

State the domain and range of the functions in the previous examples.

SOLUTION

SOLUTION

From the graph of y = –3 x – 2 + 1, you can see that the domain of the function is x 2 and the range of the function is y 1.

From the graph of y = 3 x + 2 – 1, you can see that the domain and range of the function are both all real numbers.

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Using Radical Functions in Real Life

When you use radical functions in real life, the domain is understood to be restricted to the values that make sense in the real-life situation.

The model that gives the speed s (in meters per second) necessary to keep a person pinned to the wall is

where r is the radius (in meters) of the rotor. Use a graphing calculator to graph the model. Then use the graph to estimate the radius of a rotor that spins at a speed of 8 meters per second.

s = 4.95 r

AMUSEMENT PARKS At an amusement park a ride called the rotor is a cylindrical room that spins around. The riders stand against the circular wall. When the rotor reaches the necessary speed, the floor drops out and the centrifugal force keeps the riders pinned to the wall.

AMUSEMENT PARKS At an amusement park a ride called the rotor is a cylindrical room that spins around. The riders stand against the circular wall. When the rotor reaches the necessary speed, the floor drops out and the centrifugal force keeps the riders pinned to the wall.

Modeling with a Square Root Function

SOLUTION

You get x 2.61.

The radius is about 2.61 meters.

Graph y = 4.95 x and y = 8. Choose a viewing window that shows the point where the graphs intersect. Then use the Intersect feature to find the x-coordinate of that point.

Modeling with a Cube Root Function

Use a graphing calculator to graph the model. Then use the graph to estimate the age of an elephant whose shoulder height is 200 centimeters.

SOLUTION

The elephant is about 8 years old.

You get x 7.85

Biologists have discovered that the shoulder height h (in centimeters) of a male African elephant can be modeled by

h = 62.5 t + 75.83

where t is the age (in years) of the elephant.

Graph y = 62.5 x + 75.8 and y = 200 with your calculator. Choose a viewing window that shows the point where the graphs intersect. Then use the Intersect feature to find the x-coordinate of that point.

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Assignment

Section 7.5: page 434 – 435 # 15 – 21, 24 – 45 (every

3rd), 48, 49