对于3o“、45。、6o。三个锐角的正切值同学们都已经知道,并且也会求其值.但是15。的正切值又如何求呢?下面介绍一种求法,供同学们欣赏.乙AAC解:如图,作Rt△ABc,使乙c=9o“,二300,B‘=1,则AB二2.由勾股定理得=丫厄一再延长CA到D,使AD=AB,连结BD,刀则有乙D=150,…DC=刀滩+AC=…t For 3o, 45, and 6o, the tangents of the three acute angles have been known, and they will also be worth their value. But what about the tangent of 15. How does the tangent value be sought? Here is a way to learn, for the students to appreciate. B AAC solution: as shown in the figure, for Rt △ ABc, so that B = 9o ", two 300, B’ = 1, then AB two 2. By Pythagorean Theorem = 丫 ER repeatedly extended CA to D, so that AD = AB , link BD, the knife has B = 150, ... DC = knife beach + AC = ... t