x? +4x-5≠0
Get:
X≦-5 and x≠ 1
The domain of the function is
(-∞,-5)∪(-5, 1)∪( 1,+∞)
Let g(x)=x? +4x-5
The symmetry axis is x=-2,
When x
When x >-2, g(x) increases monotonically.
According to the monotonicity of the composite function,
The increasing interval of the original function is
(-∞,-5)∪(-5,-2)
That is, the monotone decreasing interval of g(x) on the definition domain.