This requires drawing, combining graphics and shapes. When a>0, the piecewise function is incremental when X "A"; When x "a", the image first increases and then decreases, and when x = a, the image is connected. Throughout the whole function image, it first increases at (negative infinity, 3a/4), then decreases at (3a/4, a), and then increases at (a, positive infinity). According to the image, a/2 is less than or equal to m, less than 3a/4, a is less than or equal to n, less than or equal to 3/8 plus 3 times a, (there may be errors, please calculate by yourself. )

Be a<0, do it yourself.