∵? ∴? ∽? ∠? Δ? √? x⊥''

By f(x)=x-2x,

Get an f? (x)=2x-2

By f? (x)=2x-2=0

X= 1。

In (-∞, 1), f? (x)& lt； 0, and the decreasing interval is (-∞,1);

In (1, +∞), f? (x)>0, and the increment interval is (1, +∞).

therefore

F(x)=x-2x, and the decreasing interval of f is (-∞,1); The increment interval is (1, +∞).

Method 2: (mirror image method)

As shown in the figure.

To observe the image, you must

F(x)=x-2x, and the decreasing interval of f is (-∞,1); The increment interval is (1, +∞). ?