The formula for the circumference of a circle is:

`c=2pir`

And the area of a circle is:

`A=pir^2`

To express the area as a function of *c*, we need to replace the variable *r* with *c*.

To do so, isolate the *r* in the formula of the circle's...

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The formula for the circumference of a circle is:

`c=2pir`

And the area of a circle is:

`A=pir^2`

To express the area as a function of *c*, we need to replace the variable *r* with *c*.

To do so, isolate the *r* in the formula of the circle's circumference.

`c=2pir`

`r=c/(2pi)`

Then, substitute this to the formula of area of a circle.

`A=pi(c/(2pi))^2`

`A=pi*c^2/(4pi^2)`

`A=c^2/(4pi)`

**Hence, the area of a circle as a function of its circumference c is `A(c)=c^2/(4pi)` .**