Cut a round piece of paper with a diameter of 20cm into two semicircles. The circumference of each semicircle is () and the area is () (2) How big is the wall to open the arch? (two decimal places are reserved for the result)

Cut a round piece of paper with a diameter of 20cm into two semicircles. The circumference of each semicircle is () and the area is () (2) How big is the wall to open the arch? (two decimal places are reserved for the result)

Cut a round piece of paper with a diameter of 20cm into two semicircles. The circumference of each semicircle is () and the area is ()
Perimeter = 3.14 × 10 + 20 = 51.4cm
Area = 3.14 × 10 × 10 △ 2 = 314 △ 2 = 157 (square centimeter)

It is known that the circumference of a semicircle is 20.56 cm. (1) what is the radius of the semicircle? (2) What's its area?

(1) Let its radius be r cm, & nbsp; & nbsp; 2 π R2 + 2R = 20.56, & nbsp; & nbsp; & nbsp; & nbsp; π R + 2R = 20.56, & nbsp; & nbsp; 3.14r + 2R = 20.56, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 5.14r = 20.56, 5.14r △ 5.14 = 20.56 △ 5.14, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; R = 4; (2) the area of each semicircle is: 3.14 × 42 △ 2, = 3.14 × 16 △ 2, = 50.24 △ 2, = 25.12 (square centimeter); a: the area of this semicircle is 25.12 square centimeter