怎样计算半圆的周长
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\u534a\u5706\u7684\u5468\u957f\u7b49\u4e8e\u76f4\u5f84\u4e58\u4ee5\u5706\u5468\u7387\u9664\u4ee5\u4e8c
半圆的周长=2R+1/2×π×2R=(2+π)RR是半径
圆的周长除以2加半圆的直径
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