△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=
,BC=3,则△ABC的周长为( )π 3
A. 4
sin(B+
3
)+3π 3
B. 4
sin(B+
3
)+3π 6
C. 6sin(B+
)+3π 3
D. 6sin(B+
)+3 π 6
答
根据正弦定理
=BC sinA
,AC sinB
=BC sinA
AB sin(120°−B)
∴AC=sinB
=2BC sinA
sinB,AB=sin(120°−B)
3
=3cosB+BC sinA
sinB
3
∴△ABC的周长为2
sinB+3cosB+
3
sinB+3=6sin(B+
3
)+3π 6
故选D.