24.已知,在平面直角坐標(biāo)系中,A,B兩點(diǎn)的坐標(biāo)分別為點(diǎn)A(3,0),點(diǎn)B(0,b),將線段AB繞點(diǎn)A順時(shí)針旋轉(zhuǎn)α°得到AC,連接BC.
(1)若α=90.
①如圖1,b=1,直接寫出點(diǎn)C的坐標(biāo);
②如圖2,D為BC中點(diǎn),連接OD.求證:OD平分∠AOB;
(2)如圖3,若α=60,b=3,N為BC邊上一點(diǎn),M為AB延長(zhǎng)線上一點(diǎn),BM=CN,連接MN,將線段MN繞點(diǎn)N逆時(shí)針旋轉(zhuǎn)120°得到NP,連接OP.求當(dāng)∠AOP取何值時(shí),線段OP最短.