10.(1)5.8m
(2)安全
11.(1)△ABF~△FCE
(2)AD=10X ABCD=36CM
12.S=1/2AB*BCsinB
13.(1)n*1/2AnRn=NR2 sin180/n cos180/n或nS△OAB=n*1/2OA*OBsin360/n=NR2/2sin360/n
(2)周长正6 6R正12 24Rsin15°48Rsin75°
10.(1)5.8m
(2)安全
11.(1)△ABF~△FCE
(2)AD=10X ABCD=36CM
12.S=1/2AB*BCsinB
13.(1)n*1/2AnRn=NR2 sin180/n cos180/n或nS△OAB=n*1/2OA*OBsin360/n=NR2/2sin360/n
(2)周长正6 6R正12 24Rsin15°48Rsin75°