半径为R的圆内接正n边形的面积为（）A．12R2sin2πnB．n2R2sin2πnC．12R2cos2πnD．n2R2sinπn

Question

半径为R的圆内接正n边形的面积为（　　）

A．(1)/(2)R2sin(2π)/(n)
B．(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)

(1)/(2)R2sin(2π)/(n)
B．(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(1)/(2)1122R2sin(2π)/(n)
B．(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)R2sin(2π)/(n)
B．(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)2sin(2π)/(n)
B．(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(2π)/(n)2π2πnn
(n)/(2)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(n)/(2)nn22R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)R2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)2sin(2π)/(n)
C．(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(2π)/(n)2π2πnn
(1)/(2)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(1)/(2)1122R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)R2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)2cos(2π)/(n)
D．(n)/(2)R2sin(π)/(n)(2π)/(n)2π2πnn
(n)/(2)R2sin(π)/(n)(n)/(2)nn22R2sin(π)/(n)R2sin(π)/(n)2sin(π)/(n)(π)/(n)ππnn

Answer 1

半径为R的圆的内接正n边形的边长为2Rsin(π)/(n)，
边心距为Rcos(π)/(n)，
则正n边形的面积为=n•(1)/(2)2Rsin(π)/(n)•Rcos(π)/(n)=(n)/(2)R2sin(2π)/(n)
故选：B． (π)/(n)πππnnn，
边心距为Rcos(π)/(n)，
则正n边形的面积为=n•(1)/(2)2Rsin(π)/(n)•Rcos(π)/(n)=(n)/(2)R2sin(2π)/(n)
故选：B． (π)/(n)πππnnn，
则正n边形的面积为=n•(1)/(2)2Rsin(π)/(n)•Rcos(π)/(n)=(n)/(2)R2sin(2π)/(n)
故选：B． (1)/(2)1112222Rsin(π)/(n)•Rcos(π)/(n)=(n)/(2)R2sin(2π)/(n)
故选：B． (π)/(n)πππnnn•Rcos(π)/(n)=(n)/(2)R2sin(2π)/(n)
故选：B． (π)/(n)πππnnn=(n)/(2)R2sin(2π)/(n)
故选：B． (n)/(2)nnn222R2sin(2π)/(n)
故选：B． 2sin(2π)/(n)2π2π2πnnn
故选：B．