Solids.. Slice

SLICE command enables you to create a 3D cutaway view of the model.

Create a RECTANGLE and EXTRUDE it by .5 unit as shown in Figure 1

Figure 1

Figure 2

Create another SMALL YELLOW RECTANGLE as shown in Figure 2

UNION the two rectangle as shown in Figure 3

Figure 3

Figure 4

Change the object to 2D Wireframe and use SLICE command separate the two rectangle as shown in Figure 4
Invoke SLICE (Draw menu > Solids > Slice)
Command:_slice
Select objects: Click on the object and it will select both the rectangle
Select objects: Enter
Specify first point on slicing plane by [Object/Zaxis/View/XY/YZ/ZX/3points] <3points>: 3
Specify first point on plane: Click on point 1
Specify second point on plane: Click on point 2
Specify third point on plane: Click on point 3
Specify a point on desired side of the plane or [keep Both sides]: B (will keep both rectangle)

Now seperate the rectangle by using the MOVE command as shown in Figure 5.

Figure 5

SLICE the two rectangle, removing the smaller rectangle completely from Figure 6

Figure 6

Figure 7

Figure 8