由倍角公式和同角三角函数间的关系很容易证得sinα=2tanα21+tan2α2,cosα=1-tan2α21+tan2α2,tanα=2tanα21-tan2α2,这三个公式通常称之为万能公式.在万能公式中,如果令tanα2=t,则通过代换往往可以把三角问题转化为代数问题来求解;反过来,如果在一个代数问题中含有 The relationship between the multiplier angle and the trigonometric trigonometric function can be easily proved by sinα = 2tanα21 + tan2α2, cosα = 1-tan2α21 + tan2α2, tanα = 2tanα21-tan2α2, which are usually called universal formulas. , If tanα2 = t, then by replacing the triangle problem can often be transformed into algebraic problems to solve; conversely, if in an algebra problem contains