设在Rt△ABC中,∠C=90°,
（∠A,∠B,∠C的对边为a,b,c.)
且 a=5 cm,b=10 cm.
则 tan A =a/b =1/2,
tan B =b/a =2.
查表得 A=
B=
= = = = = = = = =
我没带计算器,又没有表.