Question

The radius of a circle of area a and circumference c is doubled. find the new area of the circle in terms of
a.

Answer 1

By definition, the circumference of a circle is:
 $c = 2 * pi * r$
 The area of a circle is:
 $a = pi * r ^ 2$
 Where,
 r: radius of the circle.
 When the radius is double, then the new area is:
 $A = \pi*(2r)^2$
 Rewriting we have:
 $A = 4 * \pi * r ^ 2$
 In terms of a we have:
 $A = 4 * a$
 Answer:
 The new area of the circle in terms of a is:
 $A = 4 * a$