The missing elements I guess will be circumference and area of a circle, or volume and surface area of a sphere. For these you need to know the radius. Pi is also used as a measurement of angle and pi is equivalent to 180 degrees. Instead of degrees the angle is measured in radians, so pi radians is 180 degrees. Pi is always involved with circular objects, like cones and cylinders, where height is also needed to be able to calculate surface area and volume. 3.14 is an approximation to pi which is an irrational number. Using 3.14 as pi, we have (pi)r^2 as the area of a circle=3.14r*r, its circumference 2(pi)r=6.28r; volume of sphere=4/3(pi)r^3=4.19r*r*r, its surface area=4(pi)r^2=12.56r*r. 30 degrees is (pi)/6 radians=0.52 radians.