00:01
For problem 17, we're given an expression, just like 15 and 16, where we have to determine the excluded values in our domain and also multiply and simplify the expression.
00:14
So we have x squared minus 9 over x squared times x squared minus 3x, all divided by x squared plus x minus 12.
00:25
Your textbook does want you to exclude those numbers in your domain from your original expression before you actually multiply and simplify.
00:35
So what we are going to do is just look at our denominators, x squared, and set that equal to zero, and also x squared plus x minus 12 equals zero.
00:49
So for x squared equals zero, if you take the square root of both sides, that's just going to be still, x equals zero.
00:56
And for x squared plus x minus 12 we do have to factor.
01:01
So you can use that trick where we have our two values in an x, where we put c in our top and b in our bottom portion of our chart.
01:14
We need two numbers that multiply together to give us negative 12, but add together to give us positive 1.
01:20
So that would be negative 3 and positive 4.
01:27
And then we can just split those two up, so that would be x minus 3 and x plus 4, both equal to 0.
01:39
And then we can solve each of those individually.
01:42
So x minus 3 equals 0, x plus 4 equals 0, so x equals 3 and x equals negative 4...