A.ι×(1-ι4/(πR2I02)) B.ι×(1-ι3/(90R2I02)) C.ι×(1-ι5/(90R2I02)) D.ι×(1-ι4/(90R2I02))
A.30×ι2/(πRI0) B.60×ι2/(πRI0) C.90×ι2/(πRI0) D.180×ι2/(πRI0)
A.夾直線長(zhǎng)度 B.曲線長(zhǎng) C.外矢距 D.切線長(zhǎng)