例已知△ABC内接于⊙O,(1)如图1,AD⊥BC,证明∠BAD=∠OAC;(2)运用(1)结论,如图2,H为△ABC的垂心,若∠ABC的平分线BE⊥HO,交⊙O于E,⊙O的半径为10,求弦AC的长.(1)证明如图1,延长AO交⊙O于K,连接CK.∵AK为⊙O直径,AD⊥BC,∴∠BDA=∠KCA=90°.又∠B=∠K,由三角形内角和知∠BAD=∠OAC.对于第二问,提供以下四种解题思路.思路1构造等边三角形(2)解如图3,连接BH,BO,连CH并延长交AB于G,交⊙O于F,连接BF,作直 △ ABC is known to be connected to ⊙O, (1) as shown in Figure 1, AD ⊥ BC, to prove ∠BAD = ∠ OAC; (2) to use (1) the conclusion, as shown in Figure 2, H is the vertigo of △ABC, if ∠ ABC’s bifurcation line BE⊥HO, intersect with O in E, the radius of ⊙O is 10, and find the length of the AC string. (1) Prove that as shown in Figure 1, extend AO to intersect O to K, and connect CK to AK to ⊙ O diameter, AD ⊥BC, ∴∠BDA=∠KCA=90°. Also ∠B=∠K, from the triangle inside angle and know ∠BAD=∠OAC. For the second question, provide the following four kinds of problem solving ideas. 1 Construct an equilateral triangle (2) Solution as shown in Figure 3, connect BH, BO, connect CH and extend cross AB to G, intersect O to F, connect BF, make straight