Q31 Matemática
(Tournament Of Towns 2011)
31 | Tournament Of Towns | 2011 | Matemática
Dado que
0
<
a
,
b
,
c
,
d
<
1
e
ab
c
d
=
(
1
−
a
)
(
1
−
b
)
(
1
−
c
)
(
1
−
d
)
, prove que
(
a
+
b
+
c
+
d
)
−
(
a
+
c
)
(
b
+
d
)
≥
1
