200分!快!九年级数学题目

设BD=x
则根据三角形相似可得：
1.7/AB=3/(3+x)
1.7/AB=5/(10+x)

所以3/(3+x)=5/(10+x)
x=7.5
1.7/AB=3/10.5
AB=5.95

电线干的高为5.95m

h=(10-3)*1.7/(5-3)=5.95m

设BD长度为x
然后就用相似三角形做啦
DE/BE=CD/AB
3/(X+3)=1.7/AB
GH/BH=FG/AB
5/(X+8)=1.7/AB

3/(X+3)=5/(X+8)
X=4.5 AB=4.25

由于
DE:BE=CD:AB
==>3:BE=1.7:AB (1)

GH:AH=GF:AB
==>DE:BE=CD:AB
==>5:BH=1.7:AB
==>5:(BE+GE+GH)=1.7:AB
==>5:(BE+DG-DE+GH)=1.7:AB
==>5:(BE+5-3+5)=1.7:AB
==>5:(BE+7)=1.7:AB (2)

综合(1)(2)得
3:BE=5:(BE+7)
==>BE=10.5米
代入(1)得
AB=5.95米