【導(dǎo)讀】當(dāng)d=4cm時(shí),直線l與⊙O___________;當(dāng)d=___________時(shí),直線l與⊙O相切;,,,以為圓心,rAB為半徑的圓與有何位置關(guān)系?由勾股定理得:22226810ABACBC?????當(dāng)r=6cm時(shí),8>∴直線AB與圓C相交.若⊙A與兩直線沒(méi)有公共點(diǎn),則R的取值范圍為_(kāi)_________________;km的筆直公路將兩村連通,經(jīng)測(cè)量得點(diǎn)A是圓心,水庫(kù)的半徑3km,∠ABC=45。求出其與y軸、x軸的交點(diǎn)