From YouTube, produced by Lawrence Perez/Candice Jhu
This video starts with a note that the student should watch the video on absolute numbers. The meaning of multiplication is reviewed, it is repeated addtion. Using a number line they explain how positive and negative numbers impact the equation. 3 x 1 = 1 + 1 + 1 = 3, -1 x 3 = -1 + -1 + -3. They show it this way to show that a positive times a positive is always a positive and a negative times a positive will always be negative. By the commutative property then a positive times a negative is negative. Then some examples are done. They also show another rule: multiplying a number by -1 is the same as taking the opposite of the number. They then go through a few examples. Then they go through a negative number times a negative number. The rule they discover is: negative times a negative number equals a positive number. Some examples are done. Video is good quality and good for all students as review or initial learning of the concept. There are English captions at the bottom.