The function f ( r ) = π r 2 determines the area of a circle in cm2, A , in terms of the radius of the circle in cm, r .

Question

The function  determines the area of a circle in cm², , in terms of the radius of the circle in cm, .

Use function notation to represent each of the following:

The radius (in cm) of a circle whose area is 1621 cm²?

How much larger area a circle whose radius is 15.9 cm has than a circle whose radius is 15.8 cm?

Answer 1

The radius (in cm) of a circle whose area is 1621 cm²?

1621=πr² Divide both sides by π

1621/π=πr²/π Simplify

516.2 =r² Take the square root of both sides

√516.2=√r²

r=22.7 cm

How much larger area a circle whose radius is 15.9 cm has than a circle whose radius is 15.8 cm?

A=πr²

A=π(15.9)² = 793.8

A=π(15.8)² = 783.9

793.8-783.9 = 9.9 cm² larger