Re: Trigonometric Identity

You've already shown:

$\displaystyle sin(2\theta)>0$

$\displaystyle cos(2\theta)>0$

$\displaystyle tan(2\theta)>0$

What does each of these inequalities tell you about $\displaystyle 2\theta$?

Re: Trigonometric Identity

Too be honest I am not really sure >.<

that 2 theta is positive?

Re: Trigonometric Identity

It might help if you consider $\displaystyle 2\theta$ as a single variable. That is, let $\displaystyle 2\theta=a$ (a is for angle!) Now, each of the values you calculated is positive.

What quadrants can a be in to make sin(a) positive?

What quadrants can a be in to make cos(a) positive?

What quadrants can a be in to make tan(a) positive?

Re: Trigonometric Identity

oh I get it .. so Quadrant I. Because sin, cos and tan are all positive in Quadrant I