00:01
We're given y equals the quantity of 2x squared minus 1 and 1 minus 4x.
00:14
And we're also given the tangent line, y equals 4x minus 1.
00:23
So the first thing that we need to do is figure out the derivative of this.
00:27
They actually ask you for the derivative.
00:30
So let's do this in green.
00:30
The product rule says to take the derivative of the left side.
00:33
You leave the right side alone.
00:38
Plus now you leave the left side alone and then multiply by the derivative of the right side, which would be negative 4.
00:46
So as i go to clean this up a little bit, i'll get 4x.
00:50
I'm distributing minus 16x squared.
00:55
That becomes as i distribute negative 4, oops, negative 8, 2 times negative 4.
01:07
I want to keep that as a plus negative.
01:09
And then plus 4.
01:13
I forgot my x squared.
01:16
There we go.
01:17
So as i'm looking at this, i'm seeing negative 16 minus 8 would be negative 24 x squared, plus 4x plus 4.
01:30
And what we know from giving the tangent line is that the slope of that tangent line is 4...