Solution: let the heights GE=h, CF=l and AF=a,

When x≤a,

At △OEG and △OFC,

∠GOE=∠COF (male * * * angle), ∠ AEG =∠ AFC = 90,

∴△OEG∽△OFC,OEOF=GECF，

∴ya？ (x？ y)=hl，

∴y=-hl？ hx+ahl？ h，

∫a, H and L are all fixed constants,

The coefficient of the independent variable x is a fixed value,

∴ This function image must be a linear function image, that is, a straight line;

The length of the shadow becomes shorter and shorter as it gets closer to the light, becomes a point below the light, and then becomes larger as it gets farther and farther away from the light.

So choose a.