00:01
So in this question we say at what points on the curve, x equals 4 t cubed, and y equals 4 plus 64 t minus 16 t squared, does the tangent line have a slope of 1? so if i want my tangeline to have a slope of 1, that means i want my d, y, d, d x to be equal to 1.
00:21
Now, what is dy, dx? you may recall that dydx is equal to the derivative of y with respect to, to t divided by the derivative of x with respect to t and i want this to be equal to one so my derivative of y with respect to t this time that's 64 minus 32 t over my d x d t this time that's 12 t squared i want this to be equal to one to solve this i'm going to multiply up my denominator multiply up that 12 t squared 12 t squared so that i have 64 minus 32t is equal to 12 t squared.
01:13
I'll set this equal to 0.
01:15
I'll say i've got 12 t squared plus 32 t minus 64 is equal to 0.
01:26
Now on that left -hand side, i'm going to factor out a greatest common factor.
01:31
I can factor out a 4.
01:34
If i divide both sides by four, i'm getting 3t squared plus 8t minus 16 is equal to zero.
01:46
Now at this point, i'm hoping that my left -hand side is going to factor.
01:52
And i believe this guy will factor.
01:55
Let's see how this is going to work.
01:57
So i believe i'm going to play around a little bit.
02:00
I think i've got 3t and t, and i think i have a 4.
02:05
And a 4.
02:07
I think i want, let's see, let's do t plus 4.
02:13
I think this will do it.
02:15
Because now i've got 12t minus 4t.
02:19
There's the 8t in the middle.
02:20
That's good...