00:01
Okay, so we have the equation here, x cubed plus 8x squared and then minus 9x minus 72 is equal to zero.
00:10
When i'm looking at this, if we factor this by grouping, just look at the first two terms, we can pull out an x squared.
00:16
If we do that just from the first two terms, we have x squared, and then, well, x squared times x is x cubed, x squared times 8 is 8x squared, so we get a plus 8, and then we're looking at negative 9x and negative 72, or let's see here, well, 9 goes into both 9 and 72, and since both things are negative, if we factor out a negative 9, we have negative 9 times x is negative 9x, and negative 9 times a positive 8 is going to be negative 72, so plus 8 is then equal to zero.
00:52
We can always check by distributing, and we get back the original first equation, but now, really, we have only two terms here, and in those two terms, there's a common factor of x plus 8, so we factor out x plus 8 from everything...