求助几道初三数学题1)扇形OAB的圆心角为90°,半径为R分别以OA,OB为直径在扇形内作半圆,P和Q分别表示两个阴影部

4个回答

  • 1)

    ∠ABC =∠BCD = 108

    ∠BAC =∠BCA =∠CBD =∠BDC =(180-108)/ 2 = 36

    ∠APB =∠DBC +∠ACB = 36 +36 = 72

    2)

    (A)证明:∵六边形ABCDEF是正六边形

    ∴每个内角都为120°.

    ∵∠FMH = 120°,A,M,B在一条直线上,

    ∴∠AFM +∠FMA =∠FMA +∠BMH = 60°,

    ∴∠AFM =∠BMH.

    (B)解决方案:猜想?:FM = MH.

    证明:

    ①当的重合点M和点A,∠FMB = 120°,BQ H和B点的MB的交叉点重合FM = MH.

    ②时,点M与点A,

    连接FB是不重合的,并扩展至G,使BG = BH,连接MG

    ∵∠BAF = 120°,AF = AB

    ∴∠AFB =∠FBA = 30°.

    BH = BG∠MBH =∠MBG MB = MB

    ∴△MBH≌△MBG,

    ∴∠MHB =∠MGB,MH = MG,

    ∵∠AFM =∠ BMH,∠HMB +∠MHB = 30°,

    ∴∠AFM +∠MGB = 30°,

    ∵∠AFM +∠MFB = 30°,

    ∴∠MFB =∠MGB.

    ∴FM = MG = MH.