大家知道不论a角的哪一种三角函数,都可以用万能公式把它化成tg a/2的有理式,这样就可以把问题转化为以tg a/2为变量的有理函数,往往有助于问题的解决。课本中指出了万能公式的这个作用,可惜没能多举例题说明,为引起对万能公式的重视,本文特举3例 Everyone knows that regardless of the trigonometric function of a angle, it can be converted into a rational equation of tg a/2 by the universal formula. This can turn the problem into a rational function with tg a/2, which often helps The solution to the problem. The function of the universal formula was pointed out in textbooks, but it was a pity that it failed to illustrate many examples. In order to draw attention to the universal formula, this article specifically cited 3 cases.