Notice that a grey tile and a white tile of the same value cancel each other out and make a zero. Circle around the positive x and the negative x tiles, with the tiles crossed out, labeled 0. A second circle around the positive unit and one of the negative unit tiles, with the tiles crossed out, labeled 0.
Now write an expression for the values that remain. A circle is added around the remaining 2 unit tiles.
See part (a).
Use the eTool below to solve part (a).
Click the link at right for the full version of the eTool: 7-6 HW eTool