(2012?烟台)如图,在Rt△ABC中,∠C=90°,∠A=30°,AB=2.将△ABC绕顶点A顺时针方向旋转至△AB′C′

2025-01-01 09:56:22
推荐回答(2个)
回答1:

∵Rt△ABC中,∠C=90°,∠A=30°,AB=2,
∴BC=

1
2
AB=
1
2
×2=1,AC=2×
3
2
=
3

∴∠BAB′=150°,
∴S阴影=AB扫过的扇形面积-AC扫过的扇形面积=
150×π×22
360
-
150×π×(
3
)2
360
=
12

故答案为:
12

回答2:

S阴影=S扇形BAB'+S△AB'C'-S扇形CAC'-S△ABC
易证△AB'C'≌△ABC
S阴影=S扇形BAB'-S扇形CAC'
△AB'C'≌△ABC
扇形BAB'与扇形CAC'对应的圆心角相等,均为150°
AB=2
AC=√3
S阴影=5/12*π*(4-3)=5/12*π