关于两角和与两角差的正切函数公式,一般三角学课本中都是从两角和的正弦两数公式和余弦函数公式导出,这种证明方法是比较简单的,也是学生容易接受的。但是,在定义三角两数时,我们既然采用了分别定义正弦、余弦、正切和余切这四种三角函数的方法,那末在讲加法定理的时候,是否也可以直接利用正切函数的定义来论证两角和与两角差的正 With regard to the tangent function formulas for the two angles and the difference between the two angles, general trigonometry textbooks are derived from the two-sum sine two-number formula and the cosine function formula. This kind of proof method is relatively simple and easy for students to accept. However, when we define the two numbers of triangles, since we have adopted the method of defining the four sine, cosine, tangent and cotangent trigonometric functions respectively, we can also use the definition of the tangent function to directly demonstrate the addition theorem. The difference between the two corners and the two corners