00:01
Here i want to find the tangent equation to the curve on the left given by those two equations at the point where t is pi by 4.
00:12
So, first step, let's find dx by dt.
00:17
Dx by dt is for cosine t.
00:23
Let's find dy by dt as negative 2 sine.
00:32
Then to work out d .y by dx, by the chain rule is d .y by dt times dt by dx, which is negative 2 sine t is dy by dt, and dt by dx is 1 over 4 cosine t.
00:58
That becomes negative 1 half, or sine over cos, t.
01:09
And that will be, so when t equals pi by 4, dy by d x will be negative 1 half, tan pi by 4, or tan pl by 4 is 1, tan 45, 1.
01:31
So negative 1 half is the slope of the tangent that we need.
01:38
So y equals mx plus b is my tangent, and we know negative 1 half x, plus b.
01:52
And to find the b, go back up to here, let's find the x and y coordinate when t is pi by 4.
02:00
So 4, sine of pi by 4.
02:07
Sign 45 degrees is root 2 over 2.
02:13
So it becomes 2 root 2.
02:16
Here i have two cosine pi by four.
02:21
Same thing, two times root 2 over 2...