Question

The circumference of a spherical pincushion is 2π cm. Find the surface area of the pincushion. Express your answer in terms of π.

Answer 1

The equation for circumference is C=pi*d (d=diameter)
So then we can plug in what we know:
2=pi*d
So then the diameter is equal to 2/pi (radius=1/pi)

Now the equation of surface area for a sphere is SA=4*pi*r^2
So we can plug in what we know:
SA=4*pi*(1/pi)(1/pi)
Some of the pi's cancel out so you are left with
SA=4/pi