切线条件问题在中考数学中屡见不鲜.解答它们,要注意灵活利用“圆的切线垂直于经过切点的半径”的性质.例1如图,AB是☉O的直径,CD⊥AB于点C,交☉O于点E,DF切☉O于点F.已知∠AEF=135°.(1)求证:DF∥AB; Tangent condition problems are not uncommon in the mathematics of middle school students. To answer them, pay attention to the flexible use of “circular tangent perpendicular to the radius of the tangent point ”. For example, Figure 1, AB is the diameter of ☉O, CD ⊥ AB at the point C. Intercommunicate O at point E, DF cut at O ​​at point F. Known ∠ AEF=135°. (1) Verification: DF∥AB;