The number by which the circumference is multiplied is:
2
We know that the circumference of the circle in terms of the radius r is given by:
[tex]\text{Circumference}=2\pi r[/tex]
Now, if the radius is doubled.
i.e.
[tex]r'=2r[/tex]
Hence, the circumference of the new circle is given by:
[tex]\text{Circumference of new circle}=2\pi (2r)\\\\i.e.\\\\\text{Circumference of new circle}=2(2\pi r)[/tex]
i.e.
[tex]\text{Circumference of new circle}=2\times \text{Circumference of original circle}[/tex]
The constant by which the circumference is multiplied is: 2
