设半径为r，半圆周长=2r+兀r=（2+3.14）r=5.14r=41.12，得r=8，所以半圆面积=0.5*兀*r*r=0.5*.3.14*8*8=100.48
设半径为r，C=2r+3.14*r=41.12cm，r=8cm，S=3.14*r^2=200.96cm^2
πr=41.12r=41.12/πS=1/2×C×r=422.7136/π cm²
