00:01
The underlying theme in this problem is the tangent line.
00:05
And to find the equation with tangent line, you need the, i'll write down point first.
00:10
Because they give you the ordered pair and the problem is 2 -1.
00:15
So we already have half the information that we need.
00:18
What we have to find is a slope.
00:20
And we find the slope by doing the derivative, d -y, d -x, at the ordered pair, 2 -1.
00:27
So now we can look at the problem at y to the fourth.
00:33
Minus 2x squared natural log of y minus 8x plus 4x squared y cube this is going to get ugly plus y so starting with the derivative you know 4 y cube d y d x but if you notice the next term it has a product in here so it's the product rule but the derivative of x squared is 2x so make that 4x leave natural log of y alone now you leave the 2x squared alone and the derivative of natural log of y is 1 over y, d y d y d x equals on the right side the derivative of negative 8 x is negative 8 we have another product rule so that would be 8 x y cubed plus well 3 times 4 to be 12 x squared y squared d y d y d x and the derivative of y is d y d x it's one d y d x but i've run out of room so now because this is already ugly enough i didn't do a second line is i'm going to plug in one and for all my y's two and for all of my xes and well you'll notice is one cube to still one times four is four d y the x now i'm not going to worry about this x because i know natural log of one is zero so that's that's going away and then two squared as four times that two would be negative eight one divided by one as 1.
02:17
So we have 8, d, y, d, d, x there.
02:20
And on the right side, we have negative 8.
02:23
Let's see, 8 times 2 times 1, it would be 16.
02:29
Let's see 2 squared is 4 times 1, 12 times 4 is 48, dy, dx, plus d y, dx...