00:01
Okay, for this problem, they want us to look at the polynomial p of x is equal to 6x to the 4 minus 23x cubed minus 13x of square plus 32x plus 16.
00:28
Okay.
00:29
So what do we know about the rational zeros? theorem, it says that we have the factors of the constant term.
00:40
So that could be plus a minus one, plus a minus two, plus a minus four, plus a minus eight, and plus a minus 16.
00:53
And we would also have the divisors of the leading coefficient.
00:58
So plus a minus one, plus or minus two, plus a minus three, and plus a minus six.
01:08
So what we could do is for possible guesses of zeros.
01:13
Take any of these as the numerator of a potential rational zero and these is the denominator.
01:20
So we could guess, for example, 4 over 1 and see if that's a 0.
01:26
We could do that.
01:27
So see what that value is 2.
01:32
Well, let's just look at these two terms now when we plug them in.
01:36
Let's say we just plug in 1 4.
01:38
So what do i mean by that? i mean like, we can pull an x from 4.
01:48
So we've pulled out one of them, and then we have a remainder 4 to the 3, minus 23 times 4 to the 3.
01:59
So rather than plug in, i meant pull out a factor of 4.
02:03
Because now we can just combine like terms.
02:05
We have two things, multiplying some value.
02:10
Instead of 4 over 3, we could look at that as like x to the 3.
02:15
So we'd have an x to the 3 term right here, x to the 3 term right here.
02:20
And they're both being multiplied by...
02:22
This one's multiplied by 24.
02:25
This one's multiplied by 23.
02:27
And you see how easy that is to subtract? we end up with what? we end up with just an x cube, which is a 4 cubed.
02:35
But let's actually apply this to this one.
02:39
So with this technique, we have like a...
02:43
Well, this is just a x cubed.
02:46
A 4 cubed.
02:48
So we pull out one of the factors of x, so we have a 4 times x squared, minus 13 x squared.
02:57
Okay, so now we've gone up to here.
03:01
What do we get? we get negative 9.
03:05
Let's see, we can pull out another factor of x.
03:09
That would be another x plus 32.
03:19
Actually it's kind of nice already.
03:21
You can see here.
03:22
X is negative 36 so we end up with negative 4x plus the remainder we've gone up to here the remainder well we can just plug in for it and we see that negative 16 plus 16 is equal to zero so this is indeed zero it was a good guess so now you could do a long division and you'll get another polynomial with the factor let's continue our raining streak let's try guessing seeing a combination of this and that.
03:55
Let's try 4 over 3.
03:58
So we have 4 over 3.
04:01
We can do this manipulation just like before.
04:05
We have 6 times 4 over 3.
04:11
All these cancel out.
04:13
It's just 2 times 4.
04:16
And there's the remaining 4 over 3.
04:20
4 over 3 minus 2 3 of 3.
04:29
And remember you can just treat these quantities right here as if they were x cubed so we can just combine like terms well this thing just becomes an eight so you have eight minus 23 that's that minus 15 x cubed so let's like that as minus 15 let's pull out another four over three why because we're going to continue evaluating our expression we're going to grab this over here 15 4 over 3 let's let's call it x squared.
05:07
So we're not too distracted.
05:09
Minus 13 squared.
05:14
Well, these cancel out.
05:16
We end up with a value minus 20.
05:18
So we end up with minus 33.
05:22
Pull out another 4 over 3.
05:25
Okay, and not just these x.
05:28
The other x plus 32x...