在数学教学中,充分利用典型习题引导学生进行开放性探究,对学生思维的深化及创新能力的培养往往能起到事半功倍的作用.例题　已知:如图1,AB⊥BD,CD⊥BD,垂足分别为B、D,AD和BC相交于点E,EF⊥BD,垂足为F.求证:1AB+1CD=1EF.证明　因为AB⊥BD,CD⊥BD,EF⊥BD.所以AB∥EF∥CD.所以EF In mathematics teaching, taking full advantage of typical exercises to guide students in open inquiry, students’ thinking deepening and the cultivation of innovative abilities can often play a multiplier role. Example problems are known: Figure 1, AB⊥BD, CD⊥BD, The vertical feet are respectively B, D, AD and BC intersect at point E, EF⊥BD, and the foot is F. Proof: 1AB+1CD=1EF. Prove that because AB⊥BD, CD⊥BD, EF⊥BD, AB∥ EF∥CD.So EF