Observe the graph of .
is increases as the values of
increases.
Increasing and decreasing function :
\1. If for all
in
, then
is decreasing on
.
2. If for all
in
, then
is increasing on
.
So as
is increasing on the interval
.
If the sign of the is positive than
is also positive. \ \
Therefore is also increases at the interval
.
and
.