From YouTube, produced by Lawrence Perez
The video starts with a review of general subtraction. Using the commutative property for addition they show how a + b = b + a, then they move into subtraction. When you subtract and you get a negative, you need to add more to the negative number to get the same answer. For example 7 - 2 = 9, so 7+ (-2) = 5 and 7 - 2 = 5, it is discussed what is the same in the last two equations. Adding a -2 is the same as subtracting 2. Other problems are then done. Video is good quality and good for all students as review or initial learning of the concept.