Question

If r is the radius of a circle and d is its diameter, which of the following is an equivalent formula for the circumference C=2πr?

A. C=2πd
B. C=πD
C. C=πr2
D. C=πdr

Answer 1

see
diameter = 2*radius
and circumference = 2*pi*r
r -> radius

Answer 2

so u can write
2r = d

Answer 3

But thats not even a choice

Answer 4

hint:
\[C = 2\pi r = \pi \left( {2r} \right) = ...?\]

Answer 5

see
C = 2*pi*r
as I told r = d/2
so plug tht in the equation :)
u will get
c = pi*d

Answer 6

Choice B?

Answer 7

yup :))

Answer 8

OKay thanks