Its slope =-2

The decreasing interval of function y is (-∞,-1).

(2) When-1 ≤ x

Its slope =0, that is, the function y neither increases nor decreases.

∴ The function y does not increase or decrease in the interval [- 1, 2].

(3) When x≥2, y=x+ 1-2+x=2x- 1.

∫ Its slope = 2 >; 0, that is, the function y is increasing.

The increasing interval of function y is [2, +∞)

Comprehensive (1)(2)(3) Know:

The increasing interval of the function y=|x+ 1|+|2-x| is [2, +∞).

The decreasing interval of the function y=|x+ 1|+|2-x| is (-∞,-1).