1. ## Trig Identity Problem

Assuming that is in interval evaluate

2. ## Re: Trig Identity Problem

Your pictures are all broken for me. Please post in plain text, or better yet, use LaTeX.

3. ## Re: Trig Identity Problem

U is on interval (-pi/2, 0), tan(u)=-1/3 Evaluate sin(2u)

4. ## Re: Trig Identity Problem

Originally Posted by bseymore
U is on interval (-pi/2, 0), tan(u)=-1/3 Evaluate sin(2u)
$\displaystyle sin\ 2u=\frac{2tan\ u}{1+tan^2\ u}$

5. ## Re: Trig Identity Problem

sin(2u) = 2sin(u)cos(u)

sketch a reference triangle in quad IV ... opposite side = -1 , adjacent side = 3

calculate the hypotenuse and determine the values of sin(u) and cos(u)

6. ## Re: Trig Identity Problem

Originally Posted by alexmahone
$\displaystyle sin\ 2u=\frac{2tan\ u}{1+tan^2\ u}$
Do you think you could show how you reached this answer? Thanks

7. ## Re: Trig Identity Problem

Originally Posted by bseymore
Do you think you could show how you reached this answer? Thanks
Work backwards.

$\displaystyle \frac{2tan\ u}{1+tan^2\ u}=\frac{2tan\ u}{sec^2\ u}$

$\displaystyle =2tan\ u\ cos^2\ u$

$\displaystyle =2sin\ u\ cos\ u$

$\displaystyle =sin\ 2u$