Surface area of a sphere

The 12 cm marked here goes right across the sphere — that is the diameter. The formula needs the radius.

Half of 12 is 6, so r = 6 cm.

Square the radius first. r² means r × r, not r × 2: 6 × 6 = 36.

Now four times π, times that: 4 × 3.14 is 12.56, and 12.56 × 36 = 452.16.

So the surface area is 452.16 square cm.