Therefore, a < 2 points.
At this time, the monotonous interval: negative infinity to 2 is increasing? ; 2 to 2/(a+2) is a negative number? ; A increases to positive infinity.
Similarly, one
When a=2, negative infinity and positive infinity increase. Done.
Two: if n exists, f(m)≤g(n) only needs f (m) min.
While g(n) increases from 0 to 2, and g (n) max = g (2) = 4;
If a & gt=2, f(m) increases from 0 to 1, and f (m) min = f (0) =-2a.
Similarly, if 2>a & gt=0, then f (m) min.
In a word, a & gt=-3 satisfies the condition.
Hope to adopt