00:04
Okay, the first thing you're going to do is find a slope of the tangent line at this point, and you want to find the derivative of f, which will use the quotient rule.
00:21
Sorry, quotient rule, and the way i remember it is, sorry, that says rule.
00:32
I'll get this.
00:34
Client rule.
00:36
Is low, d, high, minus high, d, low, over low, squared.
00:44
Low is the numerator, high as the numerator.
00:48
D is take the derivative up.
00:52
Low would just be x plus 1 times the derivative of the high will be 3x squared minus high, which is just x the 3rd.
01:02
And derivative of the low would be just 1 over low squared.
01:11
And once we work this out, we'll be at 3x the 3rd plus 3x squared, minus x the third over x plus 1 squared, which comes out to be 2x to the 3rd plus 3x squared over x plus 1 squared.
01:31
So that's your derivative.
01:32
And then you're going to find it at the point.
01:34
So they give you x is 1, y equals 1 half.
01:40
So you're going to take this x and plug it in to the derivative.
01:46
And you should get 2 times 1 to the 3 times 1 squared.
01:53
Over 2 squared and it'll come out to be 2 plus 3 over 4 and you get 5 4th for the slope of the tangent line.
02:06
So then they want you to write an equation of this tangent lines.
02:10
So you're going to use the x they give you, the y they give you, and the slope you just found.
02:19
And you're going to plug this into slope, intercept 1.
02:24
I'm sorry, point slip 1.
02:26
Y minus y 1 equals m times x minus x1.
02:31
Point slip 1.
02:34
So then you have 1 minus 1 half equals 5 over 4 times x minus 1.
02:40
You'll distribute your 5 4ths.
02:44
You get 5 4x minus 5 over 4.
02:50
And then all you got to just add 1 half to both sides.
02:58
And the slope of the tangent line would be 5 over 4x.
03:01
Y equals 5 over 4x.
03:03
And this will turn into minus 3 over 4.
03:10
Then in c, they want you to find the horizontal tangent ones.
03:18
And if the line is horizontal, always think i can draw z out of that.
03:24
It's slope of zero...