△ABC中,A=π3,BC=3,则△ABC的周长为(  ) A.43sin(B+π3)+3 B.43sin(B+π6)+3 C.6sin(B+π3)+3 D.6sin(B+π6)+3

问题描述:

△ABC中,A=

π
3
,BC=3,则△ABC的周长为(  )
A. 4
3
sin(B+
π
3
)+3
B. 4
3
sin(B+
π
6
)+3
C. 6sin(B+
π
3
)+3
D. 6sin(B+
π
6
)+3

根据正弦定理

BC
sinA
AC
sinB
BC
sinA
AB
sin(120°−B)

∴AC=sinB
BC
sinA
=2
3
sinB,AB=sin(120°−B)
BC
sinA
=3cosB+
3
sinB
∴△ABC的周长为2
3
sinB+3cosB+
3
sinB+3=6sin(B+
π
6
)+3
故选D.