★常用圆周率的计算 πx1=π πx2=6.28 πx3=9.42 πx4=12.56 πx5=15.70 πx6=18.84 πx7=21.98 πx8=25.12 πx9=28.26 πx10=31.40 πx11=34.54 πx12=37.68 πx16=50.24 πx18=56.52 πx20=62.80 πx25=78.50 πx32=100.48 πx36=113.04 πx49=153.86 πx64=200.96 πx81=254.34