Explanation:
the formulas can be easily found on the internet.
remember, the diameter of a circle is 2 times the radius.
so, the radius of our circle here is 4/2 = 2 cm.
circumference :
2×pi×r = 2×3.14×2 = 12.56 cm
area :
pi×r² = 3.14×2² = 3.14×4 = 12.56 cm²
hey, your teacher gave you the circle, where the circumference and the area have the same quantity ! funny !
so, make double sure you use the correct unit dimensions (remember, a distance has only one dimension, an area has 2 dimensions, and a volume has 3 dimensions).