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Since all circles are similar, a proportion can be set up using the circumference and diameter of each circle. Substitute the values [tex]$d_1=1, C_1=\pi$[/tex], and [tex]$d_2=2r$[/tex] into the proportion.

[tex]\[
\frac{C_1}{d_1}=\frac{C_2}{d_2}
\][/tex]

Which shows how to correctly solve for [tex]$C_2$[/tex], the circumference of any circle with radius [tex]$r$[/tex]?

Because [tex][tex]$\pi=\frac{C_2}{d_2}$[/tex] \Rightarrow C_2=2r\pi[/tex]

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Sagot :

Absolutely, let’s go through the steps to solve for [tex]\( C_2 \)[/tex], the circumference of a circle with radius [tex]\( r \)[/tex], given the proportion.

We know the relationship between circumference [tex]\( C \)[/tex] and diameter [tex]\( d \)[/tex] of a circle is given by the formula [tex]\( C = \pi d \)[/tex].

Given:
- [tex]\( d_1 = 1 \)[/tex]
- [tex]\( C_1 = \pi \)[/tex]
- [tex]\( d_2 = 2r \)[/tex]
- We need to solve for [tex]\( C_2 \)[/tex].

Using the provided proportion:
[tex]\[ \frac{C_1}{d_1} = \frac{C_2}{d_2} \][/tex]

Substitute the known values into the proportion:
[tex]\[ \frac{\pi}{1} = \frac{C_2}{2r} \][/tex]

Simplify the left-hand side since [tex]\(\frac{\pi}{1} = \pi\)[/tex]:
[tex]\[ \pi = \frac{C_2}{2r} \][/tex]

To isolate [tex]\( C_2 \)[/tex], multiply both sides of the equation by [tex]\( 2r \)[/tex]:
[tex]\[ C_2 = 2r \pi \][/tex]

Therefore, the circumference [tex]\( C_2 \)[/tex] of a circle with radius [tex]\( r \)[/tex] is given by:
[tex]\[ C_2 = 2r \pi \][/tex]

This equation shows that the circumference of a circle is directly proportional to its radius and confirms the well-known formula [tex]\( C = 2\pi r \)[/tex].