The monotone decreasing interval of the function y = LG [(x + 1) (3-x)] is?

The monotone decreasing interval of the function y = LG [(x + 1) (3-x)] is?

The monotone decreasing interval of (x + 1) (3-x) = - (x-1) ^ 2 + 4 is [1, + OO]
The domain of function is (- 1,3)
So the monotone decreasing interval of the function is [1,3]