00:01
Okay, i want to find this without a calculator.
00:03
At first glance, you might just think inverse cosine, cosine, they cancel out like square and square root, and the answer is simply 7 pi over 5.
00:14
But it's not quite that simple.
00:17
That's not correct.
00:18
Reason being, the inverse cosine function, the range of it has to be between 0 and pi.
00:27
So my only answer has to lie in that range.
00:32
Or inverse cosine.
00:35
Now what i can do though is look at the angle we have 7 pi by 5.
00:42
If i draw that it's over here in the third quadrant.
00:48
Here is the angle 7 pi 5 and that means my reference angle is going to be 2 pi by 5...