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中线、中位线是几何中两个很重要的概念,在很多问题中,若已知条件有中点,则常构造中位线,利用中位线将条件集中;若条件中有直角三角形,则常构造斜边的中线,利用斜边的中线等于斜边的一半解题。在很多竞赛题中有时将两者联用,使问题得以迅速解决,举例说明如下: 例1 如图1,在△ABC中,∠B=2∠C,AD⊥BC,垂足为D,M是BC的中点,AB=10厘米,求MD的长。(第七届“希望杯”初二试题)。
The midline and median line are two very important concepts in geometry. In many problems, if the conditions are known to have midpoints, the median line is often constructed, and the conditions are concentrated by using the median line; if there are right triangles in the conditions, The midline of the hypotenuse is often constructed, and the midline of the hypotenuse is equal to half of the hypotenuse. In many contests, the two are sometimes used together to solve the problem quickly. An example is illustrated as follows: Example 1 As shown in Figure 1, in △ABC, ∠B=2∠C, AD⊥BC, and the foot is D, M It is the midpoint of BC, AB=10 centimeters, seek the length of MD. (The seventh “Hope Cup” second grade questions).