If [tex]\( r \)[/tex] is the radius of a circle and [tex]\( d \)[/tex] is its diameter, which of the following is an equivalent formula for the circumference [tex]\( C \)[/tex]?

A. [tex]\( C = 2 \pi d \)[/tex]
B. [tex]\( C = 2 \pi \sigma^2 \)[/tex]
C. [tex]\( C = \pi d \)[/tex]
D. [tex]\( C = 2 \pi r d \)[/tex]



Answer :

To solve this problem, we start by recalling the standard formula for the circumference of a circle, which is given by

[tex]\[ C = 2\pi r \][/tex]

where [tex]\( r \)[/tex] is the radius of the circle. We also know that the diameter [tex]\( d \)[/tex] of the circle is related to the radius by the formula:

[tex]\[ d = 2r \][/tex]

Our goal is to express the circumference [tex]\( C \)[/tex] in terms of the diameter [tex]\( d \)[/tex].

First, substitute the expression for the diameter [tex]\( d \)[/tex] into the circumference formula:

[tex]\[ C = 2\pi r \][/tex]

Using the relationship [tex]\( d = 2r \)[/tex], we can solve for [tex]\( r \)[/tex]:

[tex]\[ r = \frac{d}{2} \][/tex]

Now substitute this expression for [tex]\( r \)[/tex] back into the formula for the circumference:

[tex]\[ C = 2\pi \left(\frac{d}{2}\right) \][/tex]

Simplifying this equation, we get:

[tex]\[ C = 2\pi \cdot \frac{d}{2} \][/tex]

[tex]\[ C = \pi d \][/tex]

Thus, the equivalent formula for the circumference in terms of the diameter is

[tex]\[ C = \pi d \][/tex]

From the given options, the correct one aligns with:

C. [tex]\( C = \pi d \)[/tex]

Therefore, the answer is option C.

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