初二数学----->相似图形(2)1.若a/b=c/d=2/5(b+d不等于0),则(a+c)/(b+d)=___________2.已知x:y:z=1/2:2/3:3/4..求(1)x/x+y-z(2)(x-y)/(y-z)

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初二数学----->相似图形(2)1.若a/b=c/d=2/5(b+d不等于0),则(a+c)/(b+d)=___________2.已知x:y:z=1/2:2/3:3/4..求(1)x/x+y-z(2)(x-y)/(y-z)
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初二数学----->相似图形(2)1.若a/b=c/d=2/5(b+d不等于0),则(a+c)/(b+d)=___________2.已知x:y:z=1/2:2/3:3/4..求(1)x/x+y-z(2)(x-y)/(y-z)
初二数学----->相似图形(2)
1.若a/b=c/d=2/5(b+d不等于0),则(a+c)/(b+d)=___________
2.已知x:y:z=1/2:2/3:3/4..
求(1)x/x+y-z
(2)(x-y)/(y-z)

初二数学----->相似图形(2)1.若a/b=c/d=2/5(b+d不等于0),则(a+c)/(b+d)=___________2.已知x:y:z=1/2:2/3:3/4..求(1)x/x+y-z(2)(x-y)/(y-z)
1.若a/b=c/d=2/5
方法一.用等比性质(a+c)/(b+d)=2/5
方法二.a=2/5*b,c=2/5*d
a+c=2/5(b+d)
(a+c)/(b+d)=2/5
2.x:y:z=1/2:2/3:3/4=6:8:9
设x=6k,y=8k,z=9k
(1)x/x+y-z=6k/(6k+8k-9k)=6k/5k=6/5
(2)(x-y)/(y-z)=(6k-8k)/(8k-9k)=-2k/(-k)=2