Question

If the number of square inches in the area of a circle is equal to the number of inches in its circumference, the diameter of the circle is
A. 4 inches
B. 3 inches
C. 1 inch
D. NONE

Answer 1

A = pi * r^2

C = pi * d

Which value for the radius fits both formulas?

Answer 2

so you want to set the area equal to the circumference ..

πr^2 = 2πr
r^2 - 2r = 0
r(r-2) = 0
r = 0 , the trivial case
or
r = 2

so the diameter is 4 inches