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解决三角形问题,常常要正确应用正弦定理与余弦定理,从而使问题获得突破.类型一与三角形的边长、内角有关的问题要点:解决这类问题关键要处理好以下两个方面(1)找出已知某边长的三角形,从中筛选出可解的三角形;(2)找要求线段所在的三角形,确定所需要条件,必要时设出所求量.例1在△ABC中,AB=5,AC=3,D为BC中点,且AD=4,求BC边长.分析:可设BC=x,再利用∠ADB与∠ADC互补,其余弦值
To solve the triangle problem, we often need to correctly apply the sine and cosine theorems, so that the problem can be broken. Type A and the triangle side length, the angle of the problem points: to solve these problems the key to deal with the following two aspects (1) to find (2) find the triangle where the line segments are located, determine the required conditions, and set the required quantities if necessary.Example 1 In △ ABC, AB = 5, AC = 3, D is the midpoint of BC, and AD = 4, and ask BC side length Analysis: Can be set BC = x, reuse ∠ ADB and ∠ ADC complementary, the cosine