Find the area of a circle if: a) its radius is 8 cm b) its diameter is 18 m.

In the case when the radius of the circle is specified in the problem, there is a formula for calculating the area of a circle.

S = π * r ^ 2;

Now we substitute the given value of the radius, given that the number π = 3, 14.

S = 3, 14 * (8 * 8) cm ^ 2;

S = 3.14 * 64 cm ^ 2;

Answer: S = 200, 96 cm ^ 2;

b) If we are given the diameter of a circle, then there is another formula for calculating its area.

S = (π * d ^ 2) / 4;

Let’s substitute the values.

S = (3, 14 * 18 ^ 2) / 4;

Answer: S = 254.34 m ^ 2;