作“辅助线”是几何证明中的关键．一道题能否顺利地解出，很大程度上取决于辅助线的添加．所以辅助线实际上是从已知到未知间的一座桥梁，搭好了就能过河，顺利到达彼岸．否则即使方向对，路线正确，中间隔了一条河，仍然到不了目的地．自然，通过添加辅助线，还可以进一... As an “auxiliary line” is the key to the geometric proof. Whether a question can be successfully solved depends largely on the addition of auxiliary lines. Therefore, the auxiliary line is actually a bridge from the known to the unknown, and it will be able to cross the river and reach the other side smoothly. Otherwise, even if the direction is correct, the route is correct, and there is a river in the middle, it still can not reach the destination. Naturally, by adding auxiliary lines, you can also enter...