1.线段AB的长为1CM,延长线段AB到C,使BC=2CM,已知D是BC的中点,则线段AD=( )CM.

1.线段AB的长为1CM,延长线段AB到C,使BC=2CM,已知D是BC的中点,则线段AD=( )CM.
2.如图,点A,B,C,D,E是直线L上顺次的五点,则BD=CD+( );CE=( )+( );BE=BC+( )+DE;BD=AD-( )=BE-( ).
3.15°=（ ）平角,八分之三周角=（ ）°,25°15′=（ ）.
12.为了比较线段AB和线段CD的大小,把线段CD移到线段AB上,使点C与点A重合,（1)当点D落在线段AB上时,AB( )CD;
(2)当点D与点B重合时,AB( )CD;
(3)当点D落在线段AB延长线时,AB( )CD.
14.在直线L上任取一点A,截取AB=16CM,再截取AC=40CM,求AB的中点D与AC的中点E之间的距离.

1.D是BC的中点,BD = 1 cm,AD = AB + BD = 1 + 1 = 2 cm
2.BD = CD + BC
CE = CD + DE
BE = BC + CD + DE
BD = AD - AB = BE - DE
3.平角=180°,15° = 1/12 平角
周角=360°,3/8周角 = 360 * 3/8 = 135°
1° = 60',25°15′=25.25°
12.(1) AB > CD
(2) AB = CD
(3) AB < CD
14.如BC在A的同一侧,AD = AB/2 = 8,AE = AC/2 = 20,DE = AE - AD = 20 - 8 = 12 cm
如BC在A的两侧,AD = AB/2 = 8,AE = AC/2 = 20,DE = AE + AD = 20 + 8 = 28 cm
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