The decreasing interval of function y = log12 (x2 − 4x − 5) is______ .

The decreasing interval of function y = log12 (x2 − 4x − 5) is______ .

∵ function y = log12 (x2 − 4x − 5), ∵ x2-4x-5 > 0, the solution is x > 5, or X < - 1. ∵ t = x2-4x-5 is a parabola with the opening upward and the axis of symmetry x = 2. Combined with the properties of composite function, we know that the decreasing interval of function y = log12 (x2 − 4x − 5) is (5, + ∞). So the answer is: (5, + ∞)