# Trig identiy prob

1. Jun 13, 2009

### geffman1

hey guys just had a test, i got a trig proof prob with cot 3u, just wondering how u break it up. thanks

2. Jun 14, 2009

### rock.freak667

Break it up into what?

the most I can tell you is that cot(3u)=1/tan(3u)

and one can use the triple angle formula for tan3u and get another equivalent expression.

3. Jun 14, 2009

### Cyosis

I take it you know $\cot u=\frac{\cos u}{\sin u}$. We could express this in a whole lot of ways. So you may want to give us the entire question or the expression you are working towards.

4. Jun 14, 2009

### HallsofIvy

As rockl.freak667 and Cyosis said, there are many different ways to "break up" such a function? What, exactly, was the statement of the problem?

I think I would be inclined to write it as cot(3u)= cot(u+ 2u) and use "sum" formulas. That's because I don't happen to remember offhand the "triple angle formula" rock.freak667 mentioned!