[b]If equals are added to equals, then the wholes are equal[br][br][/b]Imagine two identical puzzles. Every piece in both boxes is exactly the same, when you put the puzzles together then the finished puzzles will be exactly the same also.

Use the applet below to convince yourself that CN2 must be true![br][br]HINT: Use the red dots to drag the green lines onto the orange lines to show they are equal and show the sum of the green lines equals the sum of the orange lines. The blue lines allow you to adjust the length of the lines.