00:01
In this question, we want to prove this statement here.
00:04
I'm going to start with the right -hand side.
00:14
Suppose that we have our four quadrants, 1, 2, 3, 4.
00:20
In the first quadrant, all trigonals are positive.
00:25
Second quadrant, only sine is positive.
00:28
Third quadrant, only tangent is positive.
00:30
And fourth quadrant, only cosine is positive.
00:33
Now, suppose i have angle x over here.
00:40
Minus x will be over here.
00:41
You can see that sine minus x, minus x is in fourth quadrant.
00:50
So only cosine is positive...