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Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Click to edit Master title style,LOGO,复习“平行线的判定”,问题,1,什么是平行线?,1,在同一平面内,不相交的两条直线叫做平行线。,答:,判断两直线平行有几种方法?,问题,2,答:,1,,平行与同一直线的两直线平行;,2,,同位角相等,两直线平行;,3,,内错角相等,两直线平行;,4,,同旁内角相等,两直线平行;,例,1,直线,、分别平分、,()的度数为,;,()请证明()中你所给出的结论;,N,M,E,B,A,图,9,解,:,(),;()证明:如图,,、分别平分、,,,,又,,,,即,,,,,(),,,从而,(),;,N,M,E,B,A,4,1,3,2,例,2,如图,1,,在平面直角坐标系中,,AOB,是一块直角三角板,,AOB,=90,,,A,=60,,斜边,AB,x,轴,交,y,轴于点,C,.,(1),试求,BOM,的度数;,(2),如图,2,,若,OF,平分,BOM,,,ACO,的平分线交,FO,的延长线于点,P,.,求,P,的度数;,(3),如图,3,,若,ABO,绕点,O,转动(斜边,AB,与,y,轴正半轴始终有交点),在,(2),的条件下,试问,P,的度数是否发生改变?若改变,求出变化的范围;如果保持不变,求其度数,并说明理由,图,2,图,3,图,1,解:,(,1,)答:,BOM,=30,AOB,=90,,,A,+,B,=90,,,又,A,=60,B,=30,,,又,AB,x,轴,,BOM,=,B,=30,图,1,(,2,)答:,P,=30,理由:,OF,平分,BOM,,,又,2=1,,,2=15,,,AB,x,轴,,ACO,=,COM,=90,又,CP,平分,ACO,在,CON,中,,NOC,=90,,,NCO,=45,,,NCO,+,CNO,=90,,,CNO,=45,,,又,CNO,=2+,P,,,P,=30.,图,2,1,2,N,(,3,)答,: ,P,的大小不变, ,P,=30.,理由:设,BOM,=2,x, ,ACO,=2,y,AOC,=,BOM,=2,x,在,CON,中,,NOC,=90,,,NCO,+,CNO,=90,,,又,CNO,=2+,P,,,在,AOC,中, ,A,+,ACO,+,AOC,=180,即,60+2,x,+2,y,=180,x,+,y,=60,P,=30.,N,1,2,图,3,课堂练习,1,1.,如图,直线,AB,、,CD,交于点,O,,,OTAB,于,O,,,CEAB,交,CD,于点,C,,若,ECO=30,,则,DOT,等于(),课堂练习,2,已知:如图,,ab,,,1=70,,则,3,的度数为多少?,课堂小结,1,,平行与同一直线的两直线平行;,2,,同位角相等,两直线平行;,3,,内错角相等,两直线平行;,4,,同旁内角相等,两直线平行;,课后作业,如图,直线,ab,,那么,x,的度数是多少?,如图,在四边形,ABCD,中,,A=C=90,,,BE,平分,ABC,,,DF,平分,ADC,,试问,BEDF,吗?为什么?,Good bye,
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