在三角中,求角的大小,通常是通过求这个角的一个三角函数值来解决.根据三角函数的周期性,一个三角函数值对应无数个角,因此用三角函数值确定角的大小的核心问题是确定角存在的范围.例1:已知α∈(0,π),β∈(0,π),cosα=4/5,tgβ=-7,求α+β.分析因为已知条件中有taβ的值,所以用 tg(α+β)确定α+β的大小比较简单. In the triangle, the size of the angle is usually solved by finding a trigonometric function value of this angle. According to the periodicity of the trigonometric function, a trigonometric function value corresponds to an infinite number of angles, so the value of the angle of the corner is determined by the value of the trigonometric function. The problem is to determine the range in which the angle exists. Example 1: Known α∈(0,π),β∈(0,π), cosα=4/5, tgβ=-7, find α+β. Analysis because of known conditions There is taβ in the value, so using tg(α+β) to determine the size of α+β is relatively simple.