What is the circumference of a circle that has radius 7"cm" ?

4 Answers
Dec 3, 2017

Circumference = 7picm

Explanation:

Circumference = pi x d
Diameter = 7
C = pi x 7
C = 7pi cm

Dec 3, 2017

7 pi or "21.98 cm" (approx)

Explanation:

d = "7 cm"

Then

r = d/2 = "3.5 cm"

c = 2*pi*r

c = 2 * pi * "3.5 cm" = 7 pi "cm"

If you want an exact answer, you can multiply 7 by the value of pi, that is ~~3.14.

So

7 * 3.14 ~~ "21.98 cm"

Dec 3, 2017

The circumference is about 21cm

Explanation:

The circumference of a circle is about 3 times longer than the diameter.

The actual formula is C = pi xxD

The value for pi is about 3.142...

So if you just want an approximate answer, you could say that the circumference of the circle in question is about:

" "7 xx3 = 21cm

Dec 3, 2017

Approximately 22"cm". Exactly 7pi"cm"

Explanation:

The ratio between the circumference of a circle and its diameter is pi. We commonly write c = 2pir, using the radius instead and doubling it.

About 1500 years ago, a Chinese mathematician named Zu Chongzhi (祖沖之) calculated pi to approximately 7 decimal places and identified two useful rational approximations. One is 22/7, which is common in use and the other is 355/113 ~~ 3.1415929, which is less well known but very accurate for the number of digits you have to remember.

In the given example, we are told that the diameter is 7"cm". So using the common approximation pi ~~ 22/7, we find that the circumference is approximately:

22/7 * 7"cm" = 22"cm"