Exercise 4 Page 650

The circumference of a circle equals π times twice its radius. The area of a circle equals the product of π and the square of its radius.

Circumference: about 28.3cm
Area: about 63.6cm^2

Practice makes perfect

Let's consider the given circle.

We want to find the circumference and area of the circle. Let's do these things one by one.

Finding the Circumference

Recall that the circumference C of a circle equals π times twice its radius r. C = 2 π r In this case, r= 4.5. Let's substitute this value into the formula and calculate the circumference of the given circle. Remember, we are asked to use 3.14 as an estimation of π.

C = 2π r

Substitute

r= 4.5

C = 2π ( 4.5)

π ≈ 3.14

C ≈ 2( 3.14) (4.5)

Multiply

C ≈ 28.26

RoundDec

Round to 1 decimal place(s)

C ≈ 28.3

We found that C ≈ 28.3, which means that the circumference of the circle is about 28.3 centimeters.

Finding the Area

Recall that the area A of a circle equals the product of π and the square of its radius r. A = π r^2 Let's calculate the area of the given circle. Again, we will substitute 4.5 for r and 3.14 for π.

A = π r^2

Substitute

r= 4.5

A = π ( 4.5^2)

π ≈ 3.14

A ≈ 3.14 (4.5^2)

CalcPow

Calculate power

A ≈ 3.14 (20.25)

Multiply

A ≈ 63.585

RoundDec