Draw an image of three straight lines in the same coordinate system, they intersect each other, and calculate the abscissa of the intersection, which are 1, 7/5, 2 respectively. The lowest ray or line segment constitutes the image of fx. The highest point of fx (2 2,6).

So the maximum value of fx is 6.

8. Convert into a piecewise function and draw an image.

X≥0, f (x) = x2+x = (x+1/2) 2-1/4, with x=- 1/2 as the symmetry axis, (-1/2, -65438).

X<0, f (x) =-x2-x =-(x+1/2) 2+1/4, with x=- 1/2 as the symmetry axis, (-1/2,65433.

( 1)x & lt； -1/2 or x>0 increment; -1/2≤x≤0 decreases.

(2) According to the picture, the highest point of f (x) (1/2,3/4),

So f(x) is 3/4 of the maximum value of [- 1, 1/2].