Answer:
d = 4
Step-by-step explanation:
C = 2*pi r or C = pi * d
Area = pi *r^2= pi (d/2)^2 = pi * d^2 /4
So if they are numerically equal, you get
pi * d = pi * d^2 / 4 Divide both sides by pi
d = d^2 / 4 Multiply both sides by 4
4*d = d^2 Divide both sides by d
4 = d
