00:03
Okay, this question says r is 4 cosine theta.
00:07
They want me to draw a sketch and do a polar equation of the tangent line at the pole.
00:14
Polar equation of the tangent line to this curve at the pole.
00:19
You know the pole is the origin.
00:22
Anything in the form r equals 4 cosine theta is a circle on the x -axis with diameter 4.
00:29
If i wasn't sure, i could plug in some values for theta.
00:33
When theta is 0, i get that r equals 4.
00:39
When theta is pi over 2, i get r is 0.
00:43
When theta is pi, i get negative 4.
00:48
What happens is i start at theta equals 0 and i trace the top of a circle to pi over 2.
00:56
And as theta goes from pi over 2 to pi, i'm tracing negative r's, which closes the circle.
01:02
So i've traced the whole thing from 0 to pi.
01:06
They want the equation of the tangent line to this curve at zero.
01:13
And i can look at that until i have a vertical tangent line right there.
01:18
That vertical tangent line's polar equation is theta equals pi over two.
01:27
Now i'm sure they would like some calculus involved so we can go do that.
01:32
The slope of the tangent line is the main thing that we need.
01:35
The slope of the tangent line, d -y -d -x, after working a few of these, you'll see that it's r -prime, cosine theta, plus r, nope.
01:52
See, i haven't done them enough times to know them by heart.
01:55
X is r -cosine theta.
01:59
Y is r -sin -theta.
02:01
For d -y -d -x, i need the derivative of y in the top...