We see that to find the circumference of a circle we need to use the number "pi". One exploratory way to find pi would be to measure the circumference of circles and divide by their diameters, respectively. You will find that pi is approximately equal to 3.14, or 22/7. Click here to further explore pi.
Conjecture (Circumference ): If C is the circumference and D is the diameter of a circle, then there is a number p such that C=pD. Since D=2r, where r is the radius, the C=2pr.