Exercise 42 Page 625

Practice makes perfect

a The radius of a circle can be expressed as a function of its area.

In the given function,

r

represents the radius of a circle, and

A

represents its area.

r = \frac{A}{π}

We will now graph this square root function using a graphing calculator. We first press the

Y =

button and type the function in one of the rows. Notice that the variables given are

r

and

A .

When typing them we should replace

r

with

y

and

A

with

x .

y = \frac{x}{π}

Having written the function, we can push

GRAPH

to draw it.

Note that our graph is in the standard viewing window. Push the $WINDOW$ button and change the settings of the viewing window.

b We will now determine the radius of a circle with an area of

27

square inches. To find it push

2nd,

TRACE,

and choose the first option, value. Then, type the value of

x

27 .

We see that the value of $y$ is approximately $2.9$ when $x = 27 .$ In our context, it means that the radius of a circle to the nearest tenth is $2.9$ inches if it has an area of $27$ square inches.

Subchapter links

Check Your Understanding p.624

Practice and Problem Solving p.624-625

H.O.T. Problems p.625

Standardized Test Practice p.625

Spiral Review p.625

Skills Review p.625

Exercise 42 Page 625

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