Question

Explaination please.

Answer 1

@AnswerMyQuestions

Answer 2

@confluxepic

Answer 3

The reference angle is "The smallest angle that the terminal side of a given angle makes with the x-axis".
Look here:
http://www.mathopenref.com/reference-angle.html
In case of \(\frac{3\pi}{2}\) it looks like this:
http://www.wolframalpha.com/input/?i=angle+3pi%2F2
So our reference angle is \(\pi\) and since \(cos(\frac{3\pi}{2}) = 0\) then \(tan(\frac{3\pi}{2})\) is undefined because tan=sin/cos and division by 0 is undefined.