I need help on identities

Please show your own work on the problem so far so that the homework helpers know where to begin with helping you on this.

 

In what kind of problem might the expression tan x=2 occur?

 

You don't really need a formula as such. Try drawing a diagram (i.e. a right angled triangle). You know the value of the tangent of one angle, so you should be able to write down the values of two of the sides. There's a theorem that you know to find the third side-- try using this.

 

Well, the simplest way is to utilize the identity:
[tex]\tan^{2}(x)+1=\frac{1}{\cos^{2}(x)}[/tex]
If you are not familiar with that result, you should try to prove it first.

 

You don't need any identities to solve the system. Start by finding x...

 

Yes, Cristo's answer was the simplest method.

(Darn, he got it in ahead of me!)

 

Ideally, the OP would have used my hint.

 

I understand your point, but I can think of many problems involving tan x= 2 (or other values of tan x) that have nothing to do with right triangles.