问题 填空题
已知,
ab
a+b
=
1
3
, 
bc
b+c
=
1
4
ac
a+c
=
1
5
,则
1
a
+
1
b
+
1
c
=______.
答案

ab
a+b
=
1
3
, 
bc
b+c
=
1
4
ac
a+c
=
1
5

a+b
ab
=3,
b+c
bc
=4,
a+c
ac
=5,

1
a
+
1
b
=3①;
1
b
+
1
c
=4②;
1
a
+
1
c
=5③,

①+②+③得,2(

1
a
+
1
b
+
1
c
)=12,

1
a
+
1
b
+
1
c
=6,

故答案为6.

判断题
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