If the radius of the circle is doubled, by what number is the circumference multiplied?

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:

Now, if the radius is doubled.

i.e.

Hence, the circumference of the new circle is given by:

i.e.

The constant by which the circumference is multiplied is: 2

the circle graph is not a function.

step-by-step explanation:

the graph of the circle is not a function.

because for a graph to be a function, each value of x must give one value of y

in the circle, the values of x for -2< x< 2 each give 2 values of y.

hence this is not a function.