Find the monotone interval of function f (x) = 2x ^ 3-3x ^ 2-12x + 13 Why does the answer increase monotonically in the interval (- infinity, - 1) and [2, + infinity], and decrease monotonically in the interval [- 1,2]. Why does it not increase monotonically in the interval (- infinity, - 1) and (2, + infinity), but decrease monotonically in the interval (- 1,2). Why is the closed interval taken instead of the open interval

Find the monotone interval of function f (x) = 2x ^ 3-3x ^ 2-12x + 13 Why does the answer increase monotonically in the interval (- infinity, - 1) and [2, + infinity], and decrease monotonically in the interval [- 1,2]. Why does it not increase monotonically in the interval (- infinity, - 1) and (2, + infinity), but decrease monotonically in the interval (- 1,2). Why is the closed interval taken instead of the open interval

It's OK to write the monotone interval as open or closed, but it's better to write it as open. Sometimes the closed interval will make mistakes
For example, the increasing interval of y = log2 (X & # 178; - 1) should be written as (1, + ∞) and cannot be closed
Therefore, monotone interval, under the premise of finding the right endpoint, can write open interval