(选择题）在三角形ABC中,C=2B,那么sin3B/sinB=?A a/b B b/a C a/c D c/a
问题描述：
(选择题）在三角形ABC中,C=2B,那么sin3B/sinB=?A a/b B b/a C a/c D c/a
答
A
sin3B/sinB=sin(180-B-2B)/sinB=a/b
according to sinA/a=SINB/b=SINC/c
答
A
答
C=2B
A=π-C-B=π-3B
sinA=sin(π-3B)=sin3B
sin3B/sinB
=sinA/sinB
=a/b