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Mathematics
Problem
Explain why a function
f
f
f
satisfying
f
′
(
x
)
<
0
f'(x)<0
f
′
(
x
)
<
0
for every
x
x
x
in an open interval
(
a
,
b
)
(a,b)
(
a
,
b
)
must be decreasing on
(
a
,
b
)
(a,b)
(
a
,
b
)
.
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