Question

求下面圆的面积.（1）r=5cm (2)d=8dm (3)c=18.84dm

Answer 1

1、S=π*5*5=25π=78.5cm^2.

2、r=d/2=4dm.

S=π*4*4=16π=50.24dm^2.

3、r=c/(2π）=18.84/6.28=3dm,

S=π*3^2=9π=28.26dm^2.