Question

如图，已知在Rt△ABC中，∠C=90°，D是BC上一点，AC=2，CD=1 (1)若∠CAD=a,写出a的三个三角函数值；

（2）若∠B=a，求BC的长

Answer 1

(1)
AD = √ (2²+1²) =√5
sina = CD/AD = √5/5
cosa = AC/AD = 2 / √5=2√5 / 5
tana = 1/2

(2)
tana = AC/BC
BC = AC / tana = 2 / tana