圆周率速算表
3.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.14xxxxxxxxxxxxxxxxxxx2345671011121314151617181920===================6.2.4212.5615.718.8421.9825.1228.2631.434.5437.6840.8243.97.150.2453.3856.5259.6662.83.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.143.14xxxxxxxxxxxxxxxxxxx2²3²4²5²6²7²8²9²10²11²12²13²14²15²16²17²18²19²20²===================12.5628.2650.2478.5113.04153.86200.96254.34314379.94452.16530.66615.44706.5803.84907.461017.361133.541256圆周长的一半=πr半圆的周长=πr+2r=5.14r
圆环的面积=πR²-πr²=3.14×(R+r)×(R-r)